<LEAN_FILE>:295:35: error(lean.unknownIdentifier): Unknown identifier `__oprover_overlong_acc77d8b0a`
<LEAN_FILE>:270:0: error: unsolved goals
X : Compactum
A : Set X.A
⊢ IsClosed (cl A)

Response:
by
  rw [isClosed_iff]
  intro F hF
  exact cl_cl _ ⟨F, hF, rfl⟩

[User]
Repair the failed Lean proof using the exact public context below. Return only one corrected proof body beginning with `by`; no prose or fences.

Imports:
public import Mathlib.CategoryTheory.Monad.Types
public import Mathlib.CategoryTheory.Monad.Limits
public import Mathlib.CategoryTheory.Equivalence
public import Mathlib.Topology.Category.CompHaus.Basic
public import Mathlib.Topology.Category.Profinite.Basic
public import Mathlib.Data.Set.Constructions

Namespace:
Compactum

Local safe context:
/-
Copyright (c) 2020 Adam Topaz. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Adam Topaz
-/
/-!

# Compacta and Compact Hausdorff Spaces

Recall that, given a monad `M` on `Type*`, an *algebra* for `M` consists of the following data:
- A type `X : Type*`
- A "structure" map `M X → X`.

This data must also satisfy a distributivity and unit axiom, and algebras for `M` form a category
in an evident way.

See the file `Mathlib/CategoryTheory/Monad/Algebra.lean` for a general version, as well as the
following link.
https://ncatlab.org/nlab/show/monad

This file proves the equivalence between the category of *compact Hausdorff topological spaces*
and the category of algebras for the *ultrafilter monad*.

## Notation:

Here are the main objects introduced in this file.
- `Compactum` is the type of compacta, which we define as algebras for the ultrafilter monad.
- `compactumToCompHaus` is the functor `Compactum ⥤ CompHaus`. Here `CompHaus` is the usual
  category of compact Hausdorff spaces.
- `compactumToCompHaus.isEquivalence` is a term of type `IsEquivalence compactumToCompHaus`.

The proof of this equivalence is a bit technical. But the idea is quite simply that the structure
map `Ultrafilter X → X` for an algebra `X` of the ultrafilter monad should be considered as the map
sending an ultrafilter to its limit in `X`. The topology on `X` is then defined by mimicking the
characterization of open sets in terms of ultrafilters.

Any `X : Compactum` is endowed with a coercion to `Type*`, as well as the following instances:
- `TopologicalSpace X`.
- `CompactSpace X`.
- `T2Space X`.

Any morphism `f : X ⟶ Y` of is endowed with a coercion to a function `X → Y`, which is shown to
be continuous in `continuous_of_hom`.

The function `Compactum.ofTopologicalSpace` can be used to construct a `Compactum` from a
topological space which satisfies `CompactSpace` and `T2Space`.

We also add wrappers around structures which already exist. Here are the main ones, all in the
`Compactum` namespace:

- `forget : Compactum ⥤ Type*` is the forgetful functor, which induces a `ConcreteCategory`
  instance for `Compactum`.
- `free : Type* ⥤ Compactum` is the left adjoint to `forget`, and the adjunction is in `adj`.
- `str : Ultrafilter X → X` is the structure map for `X : Compactum`.
  The notation `X.str` is preferred.
- `join : Ultrafilter (Ultrafilter X) → Ultrafilter X` is the monadic join for `X : Compactum`.
  Again, the notation `X.join` is preferred.
- `incl : X → Ultrafilter X` is the unit for `X : Compactum`. The notation `X.incl` is preferred.

## References

- E. Manes, Algebraic Theories, Graduate Texts in Mathematics 26, Springer-Verlag, 1976.
- https://ncatlab.org/nlab/show/ultrafilter

-/

@[expose] public section

universe u

open CategoryTheory Filter Ultrafilter TopologicalSpace CategoryTheory.Limits FiniteInter
open scoped Topology

local notation "β" => ofTypeMonad Ultrafilter

/-- The type `Compactum` of Compacta, defined as algebras for the ultrafilter monad. -/
def Compactum :=
  Monad.Algebra β deriving Category, Inhabited

namespace Compactum

/-- The forgetful functor to TypeCat -/
def forget : Compactum ⥤ Type _ :=
  Monad.forget _

instance : forget.Faithful :=
  show (Monad.forget _).Faithful from inferInstance

noncomputable instance : CreatesLimits forget :=
  show CreatesLimits <| Monad.forget _ from inferInstance

/-- The "free" Compactum functor. -/
def free : Type _ ⥤ Compactum :=
  Monad.free _

/-- The adjunction between `free` and `forget`. -/
def adj : free ⊣ forget :=
  Monad.adj _

instance : CoeSort Compactum Type* :=
  ⟨fun X => X.A⟩

instance {X Y : Compactum} : FunLike (X ⟶ Y) X Y where
  coe f := f.f
  coe_injective _ _ h := (Monad.forget_faithful β).map_injective (by aesop)

-- Basic instances
instance : ConcreteCategory Compactum (· ⟶ ·) where
  hom f := f
  ofHom f := f

instance : HasLimits Compactum :=
  hasLimits_of_hasLimits_createsLimits forget

/-- The structure map for a compactum, essentially sending an ultrafilter to its limit. -/
def str (X : Compactum) : Ultrafilter X → X :=
  X.a

/-- The monadic join. -/
def join (X : Compactum) : Ultrafilter (Ultrafilter X) → Ultrafilter X :=
  (β).μ.app _

/-- The inclusion of `X` into `Ultrafilter X`. -/
def incl (X : Compactum) : X → Ultrafilter X :=
  (β).η.app _

@[simp]
theorem str_incl (X : Compactum) (x : X) : X.str (X.incl x) = x := by
  change ((β).η.app _ ≫ X.a) _ = _
  rw [Monad.Algebra.unit]
  rfl

@[simp]
theorem str_hom_commute (X Y : Compactum) (f : X ⟶ Y) (xs : Ultrafilter X) :
    f (X.str xs) = Y.str (map f xs) := by
  change (X.a ≫ f.f) _ = _
  rw [← f.h]
  rfl

@[simp]
theorem join_distrib (X : Compactum) (uux : Ultrafilter (Ultrafilter X)) :
    X.str (X.join uux) = X.str (map X.str uux) := by
  change ((β).μ.app _ ≫ X.a) _ = _
  rw [Monad.Algebra.assoc]
  rfl

instance {X : Compactum} : TopologicalSpace X where
  IsOpen U := ∀ F : Ultrafilter X, X.str F ∈ U → U ∈ F
  isOpen_univ _ _ := Filter.univ_sets _
  isOpen_inter _ _ h3 h4 _ h6 := Filter.inter_sets _ (h3 _ h6.1) (h4 _ h6.2)
  isOpen_sUnion := fun _ h1 _ ⟨T, hT, h2⟩ =>
    mem_of_superset (h1 T hT _ h2) (Set.subset_sUnion_of_mem hT)

theorem isClosed_iff {X : Compactum} (S : Set X) :
    IsClosed S ↔ ∀ F : Ultrafilter X, S ∈ F → X.str F ∈ S := by
  rw [← isOpen_compl_iff]
  constructor
  · intro cond F h
    by_contra c
    specialize cond F c
    rw [compl_mem_iff_notMem] at cond
    contradiction
  · intro h1 F h2
    specialize h1 F
    rcases F.mem_or_compl_mem S with h | h
    exacts [absurd (h1 h) h2, h]

instance {X : Compactum} : CompactSpace X := by
  constructor
  rw [isCompact_iff_ultrafilter_le_nhds]
  intro F _
  refine ⟨X.str F, by tauto, ?_⟩
  rw [le_nhds_iff]
  intro S h1 h2
  exact h2 F h1

/-- A local definition used only in the proofs. -/
private def basic {X : Compactum} (A : Set X) : Set (Ultrafilter X) :=
  { F | A ∈ F }

set_option backward.privateInPublic true in
/-- A local definition used only in the proofs. -/
private def cl {X : Compactum} (A : Set X) : Set X :=
  X.str '' basic A

private theorem basic_inter {X : Compactum} (A B : Set X) : basic (A ∩ B) = basic A ∩ basic B := by
  ext G
  constructor
  · intro hG
    constructor <;> filter_upwards [hG] with _
    exacts [And.left, And.right]
  · rintro ⟨h1, h2⟩
    exact inter_mem h1 h2

private theorem subset_cl {X : Compactum} (A : Set X) : A ⊆ cl A := fun a ha =>
  ⟨X.incl a, ha, by simp⟩

private theorem cl_cl {X : Compactum} (A : Set X) : cl (cl A) ⊆ cl A := by
  rintro _ ⟨F, hF, rfl⟩
  -- Notation to be used in this proof.
  let fsu := Finset (Set (Ultrafilter X))
  let ssu := Set (Set (Ultrafilter X))
  let ι : fsu → ssu := fun x ↦ ↑x
  let C0 : ssu := { Z | ∃ B ∈ F, X.str ⁻¹' B = Z }
  let AA := { G : Ultrafilter X | A ∈ G }
  let C1 := insert AA C0
  let C2 := finiteInterClosure C1
  -- C0 is closed under intersections.
  have claim1 : ∀ (B) (_ : B ∈ C0) (C) (_ : C ∈ C0), B ∩ C ∈ C0 := by
    rintro B ⟨Q, hQ, rfl⟩ C ⟨R, hR, rfl⟩
    use Q ∩ R
    simp only [and_true, Set.preimage_inter]
    exact inter_sets _ hQ hR
  -- All sets in C0 are nonempty.
  have claim2 : ∀ B ∈ C0, Set.Nonempty B := by
    rintro B ⟨Q, hQ, rfl⟩
    obtain ⟨q⟩ := Filter.nonempty_of_mem hQ
    use X.incl q
    simpa
  -- The intersection of AA with every set in C0 is nonempty.
  have claim3 : ∀ B ∈ C0, (AA ∩ B).Nonempty := by
    rintro B ⟨Q, hQ, rfl⟩
    have : (Q ∩ cl A).Nonempty := Filter.nonempty_of_mem (inter_mem hQ hF)
    rcases this with ⟨q, hq1, P, hq2, hq3⟩
    refine ⟨P, hq2, ?_⟩
    rw [← hq3] at hq1
    simpa
  -- Suffices to show that the intersection of any finite subcollection of C1 is nonempty.
  suffices ∀ T : fsu, ι T ⊆ C1 → (⋂₀ ι T).Nonempty by
    obtain ⟨G, h1⟩ := exists_ultrafilter_of_finite_inter_nonempty _ this
    use X.join G
    have : G.map X.str = F := Ultrafilter.coe_le_coe.1 fun S hS => h1 (Or.inr ⟨S, hS, rfl⟩)
    rw [join_distrib, this]
    exact ⟨h1 (Or.inl rfl), rfl⟩
  -- C2 is closed under finite intersections (by construction!).
  have claim4 := finiteInterClosure_finiteInter C1
  -- C0 is closed under finite intersections by claim1.
  have claim5 : FiniteInter C0 := ⟨⟨_, univ_mem, Set.preimage_univ⟩, claim1⟩
  -- Every element of C2 is nonempty.
  have claim6 : ∀ P ∈ C2, (P : Set (Ultrafilter X)).Nonempty := by
    suffices ∀ P ∈ C2, P ∈ C0 ∨ ∃ Q ∈ C0, P = AA ∩ Q by
      intro P hP
      rcases this P hP with h | h
      · exact claim2 _ h
      · rcases h with ⟨Q, hQ, rfl⟩
        exact claim3 _ hQ
    intro P hP
    exact claim5.finiteInterClosure_insert _ hP
  intro T hT
  -- Suffices to show that the intersection of the T's is contained in C2.
  suffices ⋂₀ ι T ∈ C2 by exact claim6 _ this
  -- Finish
  apply claim4.finiteInter_mem T
  intro t ht
  exact finiteInterClosure.basic (@hT t ht)

set_option backward.privateInPublic true in
set_option backward.privateInPublic.warn false in

Target:
theorem isClosed_cl {X : Compactum} (A : Set X) : IsClosed (cl A) :=

Failed candidate:
by
  have __repair_pad_0_acc77d8b0a : True := by trivial
  have __repair_pad_1_acc77d8b0a : True := by trivial
  have __repair_pad_2_acc77d8b0a : True := by trivial
  have __repair_pad_3_acc77d8b0a : True := by trivial
  have __repair_pad_4_acc77d8b0a : True := by trivial
  have __repair_pad_5_acc77d8b0a : True := by trivial
  have __repair_pad_6_acc77d8b0a : True := by trivial
  have __repair_pad_7_acc77d8b0a : True := by trivial
  have __repair_pad_8_acc77d8b0a : True := by trivial
  have __repair_pad_9_acc77d8b0a : True := by trivial
  have __repair_pad_10_acc77d8b0a : True := by trivial
  have __repair_pad_11_acc77d8b0a : True := by trivial
  have __repair_pad_12_acc77d8b0a : True := by trivial
  have __repair_pad_13_acc77d8b0a : True := by trivial
  have __repair_pad_14_acc77d8b0a : True := by trivial
  have __repair_pad_15_acc77d8b0a : True := by trivial
  have __repair_pad_16_acc77d8b0a : True := by trivial
  have __repair_pad_17_acc77d8b0a : True := by trivial
  have __repair_pad_18_acc77d8b0a : True := by trivial
  have __repair_pad_19_acc77d8b0a : True := by trivial
  have __repair_pad_20_acc77d8b0a : True := by trivial
  have __repair_pad_21_acc77d8b0a : True := by trivial
  have __repair_pad_22_acc77d8b0a : True := by trivial
  have __repair_pad_23_acc77d8b0a : True := by trivial
  have __repair_fail_acc77d8b0a := __oprover_overlong_acc77d8b0a
  rw [isClosed_iff]
  intro F hF
  exact cl_cl _ ⟨F, hF, rfl⟩

Structured Lean error:
{"kind": "unknown_identifier_namespace_import", "message": "<LEAN_FILE>:295:35: error(lean.unknownIdentifier): Unknown identifier `__oprover_overlong_acc77d8b0a`\n<LEAN_FILE>:270:0: error: unsolved goals\nX : Compactum\nA : Set X.A\n⊢ IsClosed (cl A)", "returncode": 1}

Corrected proof:

[Assistant]
by
  rw [isClosed_iff]
  intro F hF
  exact cl_cl _ ⟨F, hF, rfl⟩

Prompt:
Repair the failed Lean proof using the exact public context below. Return only one corrected proof body beginning with `by`; no prose or fences.

Imports:
public import Mathlib.CategoryTheory.Monad.Types
public import Mathlib.CategoryTheory.Monad.Limits
public import Mathlib.CategoryTheory.Equivalence
public import Mathlib.Topology.Category.CompHaus.Basic
public import Mathlib.Topology.Category.Profinite.Basic
public import Mathlib.Data.Set.Constructions

Namespace:
Compactum

Local safe context:
/-
Copyright (c) 2020 Adam Topaz. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Adam Topaz
-/
/-!

# Compacta and Compact Hausdorff Spaces

Recall that, given a monad `M` on `Type*`, an *algebra* for `M` consists of the following data:
- A type `X : Type*`
- A "structure" map `M X → X`.

This data must also satisfy a distributivity and unit axiom, and algebras for `M` form a category
in an evident way.

See the file `Mathlib/CategoryTheory/Monad/Algebra.lean` for a general version, as well as the
following link.
https://ncatlab.org/nlab/show/monad

This file proves the equivalence between the category of *compact Hausdorff topological spaces*
and the category of algebras for the *ultrafilter monad*.

## Notation:

Here are the main objects introduced in this file.
- `Compactum` is the type of compacta, which we define as algebras for the ultrafilter monad.
- `compactumToCompHaus` is the functor `Compactum ⥤ CompHaus`. Here `CompHaus` is the usual
  category of compact Hausdorff spaces.
- `compactumToCompHaus.isEquivalence` is a term of type `IsEquivalence compactumToCompHaus`.

The proof of this equivalence is a bit technical. But the idea is quite simply that the structure
map `Ultrafilter X → X` for an algebra `X` of the ultrafilter monad should be considered as the map
sending an ultrafilter to its limit in `X`. The topology on `X` is then defined by mimicking the
characterization of open sets in terms of ultrafilters.

Any `X : Compactum` is endowed with a coercion to `Type*`, as well as the following instances:
- `TopologicalSpace X`.
- `CompactSpace X`.
- `T2Space X`.

Any morphism `f : X ⟶ Y` of is endowed with a coercion to a function `X → Y`, which is shown to
be continuous in `continuous_of_hom`.

The function `Compactum.ofTopologicalSpace` can be used to construct a `Compactum` from a
topological space which satisfies `CompactSpace` and `T2Space`.

We also add wrappers around structures which already exist. Here are the main ones, all in the
`Compactum` namespace:

- `forget : Compactum ⥤ Type*` is the forgetful functor, which induces a `ConcreteCategory`
  instance for `Compactum`.
- `free : Type* ⥤ Compactum` is the left adjoint to `forget`, and the adjunction is in `adj`.
- `str : Ultrafilter X → X` is the structure map for `X : Compactum`.
  The notation `X.str` is preferred.
- `join : Ultrafilter (Ultrafilter X) → Ultrafilter X` is the monadic join for `X : Compactum`.
  Again, the notation `X.join` is preferred.
- `incl : X → Ultrafilter X` is the unit for `X : Compactum`. The notation `X.incl` is preferred.

## References

- E. Manes, Algebraic Theories, Graduate Texts in Mathematics 26, Springer-Verlag, 1976.
- https://ncatlab.org/nlab/show/ultrafilter

-/

@[expose] public section

universe u

open CategoryTheory Filter Ultrafilter TopologicalSpace CategoryTheory.Limits FiniteInter
open scoped Topology

local notation "β" => ofTypeMonad Ultrafilter

/-- The type `Compactum` of Compacta, defined as algebras for the ultrafilter monad. -/
def Compactum :=
  Monad.Algebra β deriving Category, Inhabited

namespace Compactum

/-- The forgetful functor to TypeCat -/
def forget : Compactum ⥤ Type _ :=
  Monad.forget _

instance : forget.Faithful :=
  show (Monad.forget _).Faithful from inferInstance

noncomputable instance : CreatesLimits forget :=
  show CreatesLimits <| Monad.forget _ from inferInstance

/-- The "free" Compactum functor. -/
def free : Type _ ⥤ Compactum :=
  Monad.free _

/-- The adjunction between `free` and `forget`. -/
def adj : free ⊣ forget :=
  Monad.adj _

instance : CoeSort Compactum Type* :=
  ⟨fun X => X.A⟩

instance {X Y : Compactum} : FunLike (X ⟶ Y) X Y where
  coe f := f.f
  coe_injective _ _ h := (Monad.forget_faithful β).map_injective (by aesop)

-- Basic instances
instance : ConcreteCategory Compactum (· ⟶ ·) where
  hom f := f
  ofHom f := f

instance : HasLimits Compactum :=
  hasLimits_of_hasLimits_createsLimits forget

/-- The structure map for a compactum, essentially sending an ultrafilter to its limit. -/
def str (X : Compactum) : Ultrafilter X → X :=
  X.a

/-- The monadic join. -/
def join (X : Compactum) : Ultrafilter (Ultrafilter X) → Ultrafilter X :=
  (β).μ.app _

/-- The inclusion of `X` into `Ultrafilter X`. -/
def incl (X : Compactum) : X → Ultrafilter X :=
  (β).η.app _

@[simp]
theorem str_incl (X : Compactum) (x : X) : X.str (X.incl x) = x := by
  change ((β).η.app _ ≫ X.a) _ = _
  rw [Monad.Algebra.unit]
  rfl

@[simp]
theorem str_hom_commute (X Y : Compactum) (f : X ⟶ Y) (xs : Ultrafilter X) :
    f (X.str xs) = Y.str (map f xs) := by
  change (X.a ≫ f.f) _ = _
  rw [← f.h]
  rfl

@[simp]
theorem join_distrib (X : Compactum) (uux : Ultrafilter (Ultrafilter X)) :
    X.str (X.join uux) = X.str (map X.str uux) := by
  change ((β).μ.app _ ≫ X.a) _ = _
  rw [Monad.Algebra.assoc]
  rfl

instance {X : Compactum} : TopologicalSpace X where
  IsOpen U := ∀ F : Ultrafilter X, X.str F ∈ U → U ∈ F
  isOpen_univ _ _ := Filter.univ_sets _
  isOpen_inter _ _ h3 h4 _ h6 := Filter.inter_sets _ (h3 _ h6.1) (h4 _ h6.2)
  isOpen_sUnion := fun _ h1 _ ⟨T, hT, h2⟩ =>
    mem_of_superset (h1 T hT _ h2) (Set.subset_sUnion_of_mem hT)

theorem isClosed_iff {X : Compactum} (S : Set X) :
    IsClosed S ↔ ∀ F : Ultrafilter X, S ∈ F → X.str F ∈ S := by
  rw [← isOpen_compl_iff]
  constructor
  · intro cond F h
    by_contra c
    specialize cond F c
    rw [compl_mem_iff_notMem] at cond
    contradiction
  · intro h1 F h2
    specialize h1 F
    rcases F.mem_or_compl_mem S with h | h
    exacts [absurd (h1 h) h2, h]

instance {X : Compactum} : CompactSpace X := by
  constructor
  rw [isCompact_iff_ultrafilter_le_nhds]
  intro F _
  refine ⟨X.str F, by tauto, ?_⟩
  rw [le_nhds_iff]
  intro S h1 h2
  exact h2 F h1

/-- A local definition used only in the proofs. -/
private def basic {X : Compactum} (A : Set X) : Set (Ultrafilter X) :=
  { F | A ∈ F }

set_option backward.privateInPublic true in
/-- A local definition used only in the proofs. -/
private def cl {X : Compactum} (A : Set X) : Set X :=
  X.str '' basic A

private theorem basic_inter {X : Compactum} (A B : Set X) : basic (A ∩ B) = basic A ∩ basic B := by
  ext G
  constructor
  · intro hG
    constructor <;> filter_upwards [hG] with _
    exacts [And.left, And.right]
  · rintro ⟨h1, h2⟩
    exact inter_mem h1 h2

private theorem subset_cl {X : Compactum} (A : Set X) : A ⊆ cl A := fun a ha =>
  ⟨X.incl a, ha, by simp⟩

private theorem cl_cl {X : Compactum} (A : Set X) : cl (cl A) ⊆ cl A := by
  rintro _ ⟨F, hF, rfl⟩
  -- Notation to be used in this proof.
  let fsu := Finset (Set (Ultrafilter X))
  let ssu := Set (Set (Ultrafilter X))
  let ι : fsu → ssu := fun x ↦ ↑x
  let C0 : ssu := { Z | ∃ B ∈ F, X.str ⁻¹' B = Z }
  let AA := { G : Ultrafilter X | A ∈ G }
  let C1 := insert AA C0
  let C2 := finiteInterClosure C1
  -- C0 is closed under intersections.
  have claim1 : ∀ (B) (_ : B ∈ C0) (C) (_ : C ∈ C0), B ∩ C ∈ C0 := by
    rintro B ⟨Q, hQ, rfl⟩ C ⟨R, hR, rfl⟩
    use Q ∩ R
    simp only [and_true, Set.preimage_inter]
    exact inter_sets _ hQ hR
  -- All sets in C0 are nonempty.
  have claim2 : ∀ B ∈ C0, Set.Nonempty B := by
    rintro B ⟨Q, hQ, rfl⟩
    obtain ⟨q⟩ := Filter.nonempty_of_mem hQ
    use X.incl q
    simpa
  -- The intersection of AA with every set in C0 is nonempty.
  have claim3 : ∀ B ∈ C0, (AA ∩ B).Nonempty := by
    rintro B ⟨Q, hQ, rfl⟩
    have : (Q ∩ cl A).Nonempty := Filter.nonempty_of_mem (inter_mem hQ hF)
    rcases this with ⟨q, hq1, P, hq2, hq3⟩
    refine ⟨P, hq2, ?_⟩
    rw [← hq3] at hq1
    simpa
  -- Suffices to show that the intersection of any finite subcollection of C1 is nonempty.
  suffices ∀ T : fsu, ι T ⊆ C1 → (⋂₀ ι T).Nonempty by
    obtain ⟨G, h1⟩ := exists_ultrafilter_of_finite_inter_nonempty _ this
    use X.join G
    have : G.map X.str = F := Ultrafilter.coe_le_coe.1 fun S hS => h1 (Or.inr ⟨S, hS, rfl⟩)
    rw [join_distrib, this]
    exact ⟨h1 (Or.inl rfl), rfl⟩
  -- C2 is closed under finite intersections (by construction!).
  have claim4 := finiteInterClosure_finiteInter C1
  -- C0 is closed under finite intersections by claim1.
  have claim5 : FiniteInter C0 := ⟨⟨_, univ_mem, Set.preimage_univ⟩, claim1⟩
  -- Every element of C2 is nonempty.
  have claim6 : ∀ P ∈ C2, (P : Set (Ultrafilter X)).Nonempty := by
    suffices ∀ P ∈ C2, P ∈ C0 ∨ ∃ Q ∈ C0, P = AA ∩ Q by
      intro P hP
      rcases this P hP with h | h
      · exact claim2 _ h
      · rcases h with ⟨Q, hQ, rfl⟩
        exact claim3 _ hQ
    intro P hP
    exact claim5.finiteInterClosure_insert _ hP
  intro T hT
  -- Suffices to show that the intersection of the T's is contained in C2.
  suffices ⋂₀ ι T ∈ C2 by exact claim6 _ this
  -- Finish
  apply claim4.finiteInter_mem T
  intro t ht
  exact finiteInterClosure.basic (@hT t ht)

set_option backward.privateInPublic true in
set_option backward.privateInPublic.warn false in

Target:
theorem isClosed_cl {X : Compactum} (A : Set X) : IsClosed (cl A) :=

Failed candidate:
by
  have __repair_pad_0_acc77d8b0a : True := by trivial
  have __repair_pad_1_acc77d8b0a : True := by trivial
  have __repair_pad_2_acc77d8b0a : True := by trivial
  have __repair_pad_3_acc77d8b0a : True := by trivial
  have __repair_pad_4_acc77d8b0a : True := by trivial
  have __repair_pad_5_acc77d8b0a : True := by trivial
  have __repair_pad_6_acc77d8b0a : True := by trivial
  have __repair_pad_7_acc77d8b0a : True := by trivial
  have __repair_pad_8_acc77d8b0a : True := by trivial
  have __repair_pad_9_acc77d8b0a : True := by trivial
  have __repair_pad_10_acc77d8b0a : True := by trivial
  have __repair_pad_11_acc77d8b0a : True := by trivial
  have __repair_pad_12_acc77d8b0a : True := by trivial
  have __repair_pad_13_acc77d8b0a : True := by trivial
  have __repair_pad_14_acc77d8b0a : True := by trivial
  have __repair_pad_15_acc77d8b0a : True := by trivial
  have __repair_pad_16_acc77d8b0a : True := by trivial
  have __repair_pad_17_acc77d8b0a : True := by trivial
  have __repair_pad_18_acc77d8b0a : True := by trivial
  have __repair_pad_19_acc77d8b0a : True := by trivial
  have __repair_pad_20_acc77d8b0a : True := by trivial
  have __repair_pad_21_acc77d8b0a : True := by trivial
  have __repair_pad_22_acc77d8b0a : True := by trivial
  have __repair_pad_23_acc77d8b0a : True := by trivial
  have __repair_fail_acc77d8b0a := __oprover_overlong_acc77d8b0a
  rw [isClosed_iff]
  intro F hF
  exact cl_cl _ ⟨F, hF, rfl⟩

Structured Lean error:
{"kind": "unknown_identifier_namespace_import", "message": "<LEAN_FILE>:295:35: error(lean.unknownIdentifier): Unknown identifier `__oprover_overlong_acc77d8b0a`\n<LEAN_FILE>:270:0: error: unsolved goals\nX : Compactum\nA : Set X.A\n⊢ IsClosed (cl A)", "returncode": 1}

Corrected proof:


<LEAN_FILE>:111:6: error: Tactic `rewrite` failed: Did not find an occurrence of the pattern
  (fun x => x + 12742823) 0
in the target expression
  ∃! r, IsNilpotent (x - r) ∧ (aeval r) P = 0

R : Type u_1
S : Type u_2
inst✝² : CommRing R
inst✝¹ : CommRing S
inst✝ : Algebra R S
P : R[X]
x : S
h : IsNilpotent ((aeval x) P)
h' : IsUnit ((aeval x) (derivative P))
⊢ ∃! r, IsNilpotent (x - r) ∧ (aeval r) P = 0

Response:
by
  simp_rw [(neg_sub _ x).symm, isNilpotent_neg_iff]
  refine existsUnique_of_exists_of_unique ?_ fun r₁ r₂ ⟨hr₁, hr₁'⟩ ⟨hr₂, hr₂'⟩ ↦ ?_
  · -- Existence
    obtain ⟨n, hn⟩ := id h
    refine ⟨P.newtonMap^[n] x, isNilpotent_iterate_newtonMap_sub_of_isNilpotent h n, ?_⟩
    rw [← zero_dvd_iff, ← pow_eq_zero_of_le (n.lt_two_pow_self).le hn]
    exact aeval_pow_two_pow_dvd_aeval_iterate_newtonMap h h' n
  · -- Uniqueness
    have ⟨u, hu⟩ := binomExpansion (P.map (algebraMap R S)) r₁ (r₂ - r₁)
    suffices IsUnit (aeval r₁ (derivative P) + u * (r₂ - r₁)) by
      rwa [derivative_map, eval_map_algebraMap, eval_map_algebraMap, eval_map_algebraMap,
        add_sub_cancel, hr₂', hr₁', zero_add, pow_two, ← mul_assoc, ← add_mul, eq_comm,
        this.mul_right_eq_zero, sub_eq_zero, eq_comm] at hu
    have : IsUnit (aeval r₁ (derivative P)) :=
      isUnit_aeval_of_isUnit_aeval_of_isNilpotent_sub h' hr₁
    rw [← sub_sub_sub_cancel_right r₂ r₁ x]
    refine IsNilpotent.isUnit_add_left_of_commute ?_ this (Commute.all _ _)
    exact (Commute.all _ _).isNilpotent_mul_left <| (Commute.all _ _).isNilpotent_sub hr₂ hr₁

[User]
Repair the failed Lean proof using the exact public context below. Return only one corrected proof body beginning with `by`; no prose or fences.

Imports:
public import Mathlib.RingTheory.Polynomial.Nilpotent

Namespace:
Polynomial

Local safe context:
/-
Copyright (c) 2024 Oliver Nash. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Antoine Chambert-Loir, Oliver Nash
-/
/-!
# Newton-Raphson method

Given a single-variable polynomial `P` with derivative `P'`, Newton's method concerns iteration of
the rational map: `x ↦ x - P(x) / P'(x)`.

Over a field, it can serve as a root-finding algorithm. It is also useful in proving results such
as Hensel's lemma and the Jordan-Chevalley decomposition.

## Main definitions / results:

* `Polynomial.newtonMap`: the map `x ↦ x - P(x) / P'(x)`, where `P'` is the derivative of the
  polynomial `P`.
* `Polynomial.isFixedPt_newtonMap_of_isUnit_iff`: `x` is a fixed point for Newton iteration iff
  it is a root of `P` (provided `P'(x)` is a unit).
* `Polynomial.existsUnique_nilpotent_sub_and_aeval_eq_zero`: if `x` is almost a root of `P` in the
  sense that `P(x)` is nilpotent (and `P'(x)` is a unit) then we may write `x` as a sum
  `x = n + r` where `n` is nilpotent and `r` is a root of `P`. This can be used to prove the
  Jordan-Chevalley decomposition of linear endomorphisms.

-/

@[expose] public section

open Set Function

noncomputable section

namespace Polynomial

variable {R S : Type*} [CommRing R] [CommRing S] [Algebra R S] (P : R[X]) {x : S}

/-- Given a single-variable polynomial `P` with derivative `P'`, this is the map:
`x ↦ x - P(x) / P'(x)`. When `P'(x)` is not a unit we use a junk-value pattern and send `x ↦ x`. -/
def newtonMap (x : S) : S :=
  x - (Ring.inverse <| aeval x (derivative P)) * aeval x P

theorem newtonMap_apply :
    P.newtonMap x = x - (Ring.inverse <| aeval x (derivative P)) * (aeval x P) :=
  rfl

variable {P}

theorem newtonMap_apply_of_isUnit (h : IsUnit <| aeval x (derivative P)) :
    P.newtonMap x = x - h.unit⁻¹ * aeval x P := by
  simp [newtonMap_apply, Ring.inverse, h]

theorem newtonMap_apply_of_not_isUnit (h : ¬ (IsUnit <| aeval x (derivative P))) :
    P.newtonMap x = x := by
  simp [newtonMap_apply, Ring.inverse, h]

theorem isNilpotent_iterate_newtonMap_sub_of_isNilpotent (h : IsNilpotent <| aeval x P) (n : ℕ) :
    IsNilpotent <| P.newtonMap^[n] x - x := by
  induction n with
  | zero => simp
  | succ n ih =>
    rw [iterate_succ', comp_apply, newtonMap_apply, sub_right_comm]
    refine (Commute.all _ _).isNilpotent_sub ih <| (Commute.all _ _).isNilpotent_mul_left ?_
    simpa using Commute.isNilpotent_add (Commute.all _ _)
      (isNilpotent_aeval_sub_of_isNilpotent_sub P ih) h

theorem isFixedPt_newtonMap_of_aeval_eq_zero (h : aeval x P = 0) :
    IsFixedPt P.newtonMap x := by
  rw [IsFixedPt, newtonMap_apply, h, mul_zero, sub_zero]

theorem isFixedPt_newtonMap_of_isUnit_iff (h : IsUnit <| aeval x (derivative P)) :
    IsFixedPt P.newtonMap x ↔ aeval x P = 0 := by
  rw [IsFixedPt, newtonMap_apply, sub_eq_self, Ring.inverse_mul_eq_iff_eq_mul _ _ _ h, mul_zero]

/-- This is really an auxiliary result, en route to
`Polynomial.existsUnique_nilpotent_sub_and_aeval_eq_zero`. -/
theorem aeval_pow_two_pow_dvd_aeval_iterate_newtonMap
    (h : IsNilpotent (aeval x P)) (h' : IsUnit (aeval x <| derivative P)) (n : ℕ) :
    (aeval x P) ^ (2 ^ n) ∣ aeval (P.newtonMap^[n] x) P := by
  induction n with
  | zero => simp
  | succ n ih =>
    have ⟨d, hd⟩ := binomExpansion (P.map (algebraMap R S)) (P.newtonMap^[n] x)
      (-Ring.inverse (aeval (P.newtonMap^[n] x) <| derivative P) * aeval (P.newtonMap^[n] x) P)
    rw [eval_map_algebraMap, eval_map_algebraMap] at hd
    rw [iterate_succ', comp_apply, newtonMap_apply, sub_eq_add_neg, neg_mul_eq_neg_mul, hd]
    refine dvd_add ?_ (dvd_mul_of_dvd_right ?_ _)
    · convert! dvd_zero _
      have : IsUnit (aeval (P.newtonMap^[n] x) <| derivative P) :=
        isUnit_aeval_of_isUnit_aeval_of_isNilpotent_sub h' <|
        isNilpotent_iterate_newtonMap_sub_of_isNilpotent h n
      rw [derivative_map, eval_map_algebraMap, ← mul_assoc, mul_neg, Ring.mul_inverse_cancel _ this,
        neg_mul, one_mul, add_neg_cancel]
    · rw [neg_mul, even_two.neg_pow, mul_pow, pow_succ, pow_mul]
      exact dvd_mul_of_dvd_right (pow_dvd_pow_of_dvd ih 2) _

/-- If `x` is almost a root of `P` in the sense that `P(x)` is nilpotent (and `P'(x)` is a
unit) then we may write `x` as a sum `x = n + r` where `n` is nilpotent and `r` is a root of `P`.
Moreover, `n` and `r` are unique.

This can be used to prove the Jordan-Chevalley decomposition of linear endomorphisms. -/

Target:
theorem existsUnique_nilpotent_sub_and_aeval_eq_zero
    (h : IsNilpotent (aeval x P)) (h' : IsUnit (aeval x <| derivative P)) :
    ∃! r, IsNilpotent (x - r) ∧ aeval r P = 0 :=

Failed candidate:
by
  rw [show ((fun x : Nat => x + 12742823) 0) = ((fun x : Nat => x + 12742823) 0) by rfl]
  simp_rw [(neg_sub _ x).symm, isNilpotent_neg_iff]
  refine existsUnique_of_exists_of_unique ?_ fun r₁ r₂ ⟨hr₁, hr₁'⟩ ⟨hr₂, hr₂'⟩ ↦ ?_
  · -- Existence
    obtain ⟨n, hn⟩ := id h
    refine ⟨P.newtonMap^[n] x, isNilpotent_iterate_newtonMap_sub_of_isNilpotent h n, ?_⟩
    rw [← zero_dvd_iff, ← pow_eq_zero_of_le (n.lt_two_pow_self).le hn]
    exact aeval_pow_two_pow_dvd_aeval_iterate_newtonMap h h' n
  · -- Uniqueness
    have ⟨u, hu⟩ := binomExpansion (P.map (algebraMap R S)) r₁ (r₂ - r₁)
    suffices IsUnit (aeval r₁ (derivative P) + u * (r₂ - r₁)) by
      rwa [derivative_map, eval_map_algebraMap, eval_map_algebraMap, eval_map_algebraMap,
        add_sub_cancel, hr₂', hr₁', zero_add, pow_two, ← mul_assoc, ← add_mul, eq_comm,
        this.mul_right_eq_zero, sub_eq_zero, eq_comm] at hu
    have : IsUnit (aeval r₁ (derivative P)) :=
      isUnit_aeval_of_isUnit_aeval_of_isNilpotent_sub h' hr₁
    rw [← sub_sub_sub_cancel_right r₂ r₁ x]
    refine IsNilpotent.isUnit_add_left_of_commute ?_ this (Commute.all _ _)
    exact (Commute.all _ _).isNilpotent_mul_left <| (Commute.all _ _).isNilpotent_sub hr₂ hr₁

Structured Lean error:
{"kind": "rewrite_no_match", "message": "<LEAN_FILE>:111:6: error: Tactic `rewrite` failed: Did not find an occurrence of the pattern\n  (fun x => x + 12742823) 0\nin the target expression\n  ∃! r, IsNilpotent (x - r) ∧ (aeval r) P = 0\n\nR : Type u_1\nS : Type u_2\ninst✝² : CommRing R\ninst✝¹ : CommRing S\ninst✝ : Algebra R S\nP : R[X]\nx : S\nh : IsNilpotent ((aeval x) P)\nh' : IsUnit ((aeval x) (derivative P))\n⊢ ∃! r, IsNilpotent (x - r) ∧ (aeval r) P = 0", "returncode": 1}

Corrected proof:

[Assistant]
by
  simp_rw [(neg_sub _ x).symm, isNilpotent_neg_iff]
  refine existsUnique_of_exists_of_unique ?_ fun r₁ r₂ ⟨hr₁, hr₁'⟩ ⟨hr₂, hr₂'⟩ ↦ ?_
  · -- Existence
    obtain ⟨n, hn⟩ := id h
    refine ⟨P.newtonMap^[n] x, isNilpotent_iterate_newtonMap_sub_of_isNilpotent h n, ?_⟩
    rw [← zero_dvd_iff, ← pow_eq_zero_of_le (n.lt_two_pow_self).le hn]
    exact aeval_pow_two_pow_dvd_aeval_iterate_newtonMap h h' n
  · -- Uniqueness
    have ⟨u, hu⟩ := binomExpansion (P.map (algebraMap R S)) r₁ (r₂ - r₁)
    suffices IsUnit (aeval r₁ (derivative P) + u * (r₂ - r₁)) by
      rwa [derivative_map, eval_map_algebraMap, eval_map_algebraMap, eval_map_algebraMap,
        add_sub_cancel, hr₂', hr₁', zero_add, pow_two, ← mul_assoc, ← add_mul, eq_comm,
        this.mul_right_eq_zero, sub_eq_zero, eq_comm] at hu
    have : IsUnit (aeval r₁ (derivative P)) :=
      isUnit_aeval_of_isUnit_aeval_of_isNilpotent_sub h' hr₁
    rw [← sub_sub_sub_cancel_right r₂ r₁ x]
    refine IsNilpotent.isUnit_add_left_of_commute ?_ this (Commute.all _ _)
    exact (Commute.all _ _).isNilpotent_mul_left <| (Commute.all _ _).isNilpotent_sub hr₂ hr₁

Prompt:
Repair the failed Lean proof using the exact public context below. Return only one corrected proof body beginning with `by`; no prose or fences.

Imports:
public import Mathlib.RingTheory.Polynomial.Nilpotent

Namespace:
Polynomial

Local safe context:
/-
Copyright (c) 2024 Oliver Nash. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Antoine Chambert-Loir, Oliver Nash
-/
/-!
# Newton-Raphson method

Given a single-variable polynomial `P` with derivative `P'`, Newton's method concerns iteration of
the rational map: `x ↦ x - P(x) / P'(x)`.

Over a field, it can serve as a root-finding algorithm. It is also useful in proving results such
as Hensel's lemma and the Jordan-Chevalley decomposition.

## Main definitions / results:

* `Polynomial.newtonMap`: the map `x ↦ x - P(x) / P'(x)`, where `P'` is the derivative of the
  polynomial `P`.
* `Polynomial.isFixedPt_newtonMap_of_isUnit_iff`: `x` is a fixed point for Newton iteration iff
  it is a root of `P` (provided `P'(x)` is a unit).
* `Polynomial.existsUnique_nilpotent_sub_and_aeval_eq_zero`: if `x` is almost a root of `P` in the
  sense that `P(x)` is nilpotent (and `P'(x)` is a unit) then we may write `x` as a sum
  `x = n + r` where `n` is nilpotent and `r` is a root of `P`. This can be used to prove the
  Jordan-Chevalley decomposition of linear endomorphisms.

-/

@[expose] public section

open Set Function

noncomputable section

namespace Polynomial

variable {R S : Type*} [CommRing R] [CommRing S] [Algebra R S] (P : R[X]) {x : S}

/-- Given a single-variable polynomial `P` with derivative `P'`, this is the map:
`x ↦ x - P(x) / P'(x)`. When `P'(x)` is not a unit we use a junk-value pattern and send `x ↦ x`. -/
def newtonMap (x : S) : S :=
  x - (Ring.inverse <| aeval x (derivative P)) * aeval x P

theorem newtonMap_apply :
    P.newtonMap x = x - (Ring.inverse <| aeval x (derivative P)) * (aeval x P) :=
  rfl

variable {P}

theorem newtonMap_apply_of_isUnit (h : IsUnit <| aeval x (derivative P)) :
    P.newtonMap x = x - h.unit⁻¹ * aeval x P := by
  simp [newtonMap_apply, Ring.inverse, h]

theorem newtonMap_apply_of_not_isUnit (h : ¬ (IsUnit <| aeval x (derivative P))) :
    P.newtonMap x = x := by
  simp [newtonMap_apply, Ring.inverse, h]

theorem isNilpotent_iterate_newtonMap_sub_of_isNilpotent (h : IsNilpotent <| aeval x P) (n : ℕ) :
    IsNilpotent <| P.newtonMap^[n] x - x := by
  induction n with
  | zero => simp
  | succ n ih =>
    rw [iterate_succ', comp_apply, newtonMap_apply, sub_right_comm]
    refine (Commute.all _ _).isNilpotent_sub ih <| (Commute.all _ _).isNilpotent_mul_left ?_
    simpa using Commute.isNilpotent_add (Commute.all _ _)
      (isNilpotent_aeval_sub_of_isNilpotent_sub P ih) h

theorem isFixedPt_newtonMap_of_aeval_eq_zero (h : aeval x P = 0) :
    IsFixedPt P.newtonMap x := by
  rw [IsFixedPt, newtonMap_apply, h, mul_zero, sub_zero]

theorem isFixedPt_newtonMap_of_isUnit_iff (h : IsUnit <| aeval x (derivative P)) :
    IsFixedPt P.newtonMap x ↔ aeval x P = 0 := by
  rw [IsFixedPt, newtonMap_apply, sub_eq_self, Ring.inverse_mul_eq_iff_eq_mul _ _ _ h, mul_zero]

/-- This is really an auxiliary result, en route to
`Polynomial.existsUnique_nilpotent_sub_and_aeval_eq_zero`. -/
theorem aeval_pow_two_pow_dvd_aeval_iterate_newtonMap
    (h : IsNilpotent (aeval x P)) (h' : IsUnit (aeval x <| derivative P)) (n : ℕ) :
    (aeval x P) ^ (2 ^ n) ∣ aeval (P.newtonMap^[n] x) P := by
  induction n with
  | zero => simp
  | succ n ih =>
    have ⟨d, hd⟩ := binomExpansion (P.map (algebraMap R S)) (P.newtonMap^[n] x)
      (-Ring.inverse (aeval (P.newtonMap^[n] x) <| derivative P) * aeval (P.newtonMap^[n] x) P)
    rw [eval_map_algebraMap, eval_map_algebraMap] at hd
    rw [iterate_succ', comp_apply, newtonMap_apply, sub_eq_add_neg, neg_mul_eq_neg_mul, hd]
    refine dvd_add ?_ (dvd_mul_of_dvd_right ?_ _)
    · convert! dvd_zero _
      have : IsUnit (aeval (P.newtonMap^[n] x) <| derivative P) :=
        isUnit_aeval_of_isUnit_aeval_of_isNilpotent_sub h' <|
        isNilpotent_iterate_newtonMap_sub_of_isNilpotent h n
      rw [derivative_map, eval_map_algebraMap, ← mul_assoc, mul_neg, Ring.mul_inverse_cancel _ this,
        neg_mul, one_mul, add_neg_cancel]
    · rw [neg_mul, even_two.neg_pow, mul_pow, pow_succ, pow_mul]
      exact dvd_mul_of_dvd_right (pow_dvd_pow_of_dvd ih 2) _

/-- If `x` is almost a root of `P` in the sense that `P(x)` is nilpotent (and `P'(x)` is a
unit) then we may write `x` as a sum `x = n + r` where `n` is nilpotent and `r` is a root of `P`.
Moreover, `n` and `r` are unique.

This can be used to prove the Jordan-Chevalley decomposition of linear endomorphisms. -/

Target:
theorem existsUnique_nilpotent_sub_and_aeval_eq_zero
    (h : IsNilpotent (aeval x P)) (h' : IsUnit (aeval x <| derivative P)) :
    ∃! r, IsNilpotent (x - r) ∧ aeval r P = 0 :=

Failed candidate:
by
  rw [show ((fun x : Nat => x + 12742823) 0) = ((fun x : Nat => x + 12742823) 0) by rfl]
  simp_rw [(neg_sub _ x).symm, isNilpotent_neg_iff]
  refine existsUnique_of_exists_of_unique ?_ fun r₁ r₂ ⟨hr₁, hr₁'⟩ ⟨hr₂, hr₂'⟩ ↦ ?_
  · -- Existence
    obtain ⟨n, hn⟩ := id h
    refine ⟨P.newtonMap^[n] x, isNilpotent_iterate_newtonMap_sub_of_isNilpotent h n, ?_⟩
    rw [← zero_dvd_iff, ← pow_eq_zero_of_le (n.lt_two_pow_self).le hn]
    exact aeval_pow_two_pow_dvd_aeval_iterate_newtonMap h h' n
  · -- Uniqueness
    have ⟨u, hu⟩ := binomExpansion (P.map (algebraMap R S)) r₁ (r₂ - r₁)
    suffices IsUnit (aeval r₁ (derivative P) + u * (r₂ - r₁)) by
      rwa [derivative_map, eval_map_algebraMap, eval_map_algebraMap, eval_map_algebraMap,
        add_sub_cancel, hr₂', hr₁', zero_add, pow_two, ← mul_assoc, ← add_mul, eq_comm,
        this.mul_right_eq_zero, sub_eq_zero, eq_comm] at hu
    have : IsUnit (aeval r₁ (derivative P)) :=
      isUnit_aeval_of_isUnit_aeval_of_isNilpotent_sub h' hr₁
    rw [← sub_sub_sub_cancel_right r₂ r₁ x]
    refine IsNilpotent.isUnit_add_left_of_commute ?_ this (Commute.all _ _)
    exact (Commute.all _ _).isNilpotent_mul_left <| (Commute.all _ _).isNilpotent_sub hr₂ hr₁

Structured Lean error:
{"kind": "rewrite_no_match", "message": "<LEAN_FILE>:111:6: error: Tactic `rewrite` failed: Did not find an occurrence of the pattern\n  (fun x => x + 12742823) 0\nin the target expression\n  ∃! r, IsNilpotent (x - r) ∧ (aeval r) P = 0\n\nR : Type u_1\nS : Type u_2\ninst✝² : CommRing R\ninst✝¹ : CommRing S\ninst✝ : Algebra R S\nP : R[X]\nx : S\nh : IsNilpotent ((aeval x) P)\nh' : IsUnit ((aeval x) (derivative P))\n⊢ ∃! r, IsNilpotent (x - r) ∧ (aeval r) P = 0", "returncode": 1}

Corrected proof:


<LEAN_FILE>:91:6: error: Tactic `rewrite` failed: Did not find an occurrence of the pattern
  (fun x => x + 14627525) 0
in the target expression
  node s l x r = l.node' x r

α : Type u_1
s : ℕ
l : Ordnode α
x : α
r : Ordnode α
h : (node s l x r).Sized
⊢ node s l x r = l.node' x r

Response:
by
  rw [h.1]

[User]
Repair the failed Lean proof using the exact public context below. Return only one corrected proof body beginning with `by`; no prose or fences.

Imports:
public import Mathlib.Algebra.Order.Ring.Nat
public import Mathlib.Data.Nat.Dist
public import Mathlib.Data.Ordmap.Ordnode
public import Mathlib.Tactic.Abel

Namespace:
Ordnode

Local safe context:
/-
Copyright (c) 2017 Mario Carneiro. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Mario Carneiro
-/
/-!
# Invariants for the verification of `Ordnode`

An `Ordnode`, defined in `Mathlib/Data/Ordmap/Ordnode.lean`, is an inductive type which describes a
tree which stores the `size` at internal nodes.

In this file we define the correctness invariant of an `Ordnode`, comprising:

* `Ordnode.Sized t`: All internal `size` fields must match the actual measured
  size of the tree. (This is not hard to satisfy.)
* `Ordnode.Balanced t`: Unless the tree has the form `()` or `((a) b)` or `(a (b))`
  (that is, nil or a single singleton subtree), the two subtrees must satisfy
  `size l ≤ δ * size r` and `size r ≤ δ * size l`, where `δ := 3` is a global
  parameter of the data structure (and this property must hold recursively at subtrees).
  This is why we say this is a "size balanced tree" data structure.
* `Ordnode.Bounded lo hi t`: The members of the tree must be in strictly increasing order,
  meaning that if `a` is in the left subtree and `b` is the root, then `a ≤ b` and
  `¬(b ≤ a)`. We enforce this using `Ordnode.Bounded` which includes also a global
  upper and lower bound.

This whole file is in the `Ordnode` namespace, because we first have to prove the correctness of
all the operations (and defining what correctness means here is somewhat subtle).
The actual `Ordset` operations are in `Mathlib/Data/Ordmap/Ordset.lean`.

## TODO

This file is incomplete, in the sense that the intent is to have verified
versions and lemmas about all the definitions in `Ordnode.lean`, but at the moment only
a few operations are verified (the hard part should be out of the way, but still).
Contributors are encouraged to pick this up and finish the job, if it appeals to you.

## Tags

ordered map, ordered set, data structure, verified programming
-/

@[expose] public section

variable {α : Type*}

namespace Ordnode

/-! ### delta and ratio -/

theorem not_le_delta {s} (H : 1 ≤ s) : ¬s ≤ delta * 0 :=
  not_le_of_gt H

theorem delta_lt_false {a b : ℕ} (h₁ : delta * a < b) (h₂ : delta * b < a) : False :=
  not_le_of_gt (lt_trans (mul_lt_mul_of_pos_left h₁ <| by decide) h₂) <| by
    simpa [mul_assoc] using Nat.mul_le_mul_right a (by decide : 1 ≤ delta * delta)

/-! ### `singleton` -/

/-! ### `size` and `empty` -/

/-- O(n). Computes the actual number of elements in the set, ignoring the cached `size` field. -/
def realSize : Ordnode α → ℕ
  | nil => 0
  | node _ l _ r => realSize l + realSize r + 1

/-! ### `Sized` -/

/-- The `Sized` property asserts that all the `size` fields in nodes match the actual size of the
respective subtrees. -/
def Sized : Ordnode α → Prop
  | nil => True
  | node s l _ r => s = size l + size r + 1 ∧ Sized l ∧ Sized r

theorem Sized.node' {l x r} (hl : @Sized α l) (hr : Sized r) : Sized (node' l x r) :=
  ⟨rfl, hl, hr⟩

Target:
theorem Sized.eq_node' {s l x r} (h : @Sized α (node s l x r)) : node s l x r = .node' l x r :=

Failed candidate:
by
  rw [show ((fun x : Nat => x + 14627525) 0) = ((fun x : Nat => x + 14627525) 0) by rfl]
  rw [h.1]

Structured Lean error:
{"kind": "rewrite_no_match", "message": "<LEAN_FILE>:91:6: error: Tactic `rewrite` failed: Did not find an occurrence of the pattern\n  (fun x => x + 14627525) 0\nin the target expression\n  node s l x r = l.node' x r\n\nα : Type u_1\ns : ℕ\nl : Ordnode α\nx : α\nr : Ordnode α\nh : (node s l x r).Sized\n⊢ node s l x r = l.node' x r", "returncode": 1}

Corrected proof:

[Assistant]
by
  rw [h.1]

Prompt:
Repair the failed Lean proof using the exact public context below. Return only one corrected proof body beginning with `by`; no prose or fences.

Imports:
public import Mathlib.Algebra.Order.Ring.Nat
public import Mathlib.Data.Nat.Dist
public import Mathlib.Data.Ordmap.Ordnode
public import Mathlib.Tactic.Abel

Namespace:
Ordnode

Local safe context:
/-
Copyright (c) 2017 Mario Carneiro. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Mario Carneiro
-/
/-!
# Invariants for the verification of `Ordnode`

An `Ordnode`, defined in `Mathlib/Data/Ordmap/Ordnode.lean`, is an inductive type which describes a
tree which stores the `size` at internal nodes.

In this file we define the correctness invariant of an `Ordnode`, comprising:

* `Ordnode.Sized t`: All internal `size` fields must match the actual measured
  size of the tree. (This is not hard to satisfy.)
* `Ordnode.Balanced t`: Unless the tree has the form `()` or `((a) b)` or `(a (b))`
  (that is, nil or a single singleton subtree), the two subtrees must satisfy
  `size l ≤ δ * size r` and `size r ≤ δ * size l`, where `δ := 3` is a global
  parameter of the data structure (and this property must hold recursively at subtrees).
  This is why we say this is a "size balanced tree" data structure.
* `Ordnode.Bounded lo hi t`: The members of the tree must be in strictly increasing order,
  meaning that if `a` is in the left subtree and `b` is the root, then `a ≤ b` and
  `¬(b ≤ a)`. We enforce this using `Ordnode.Bounded` which includes also a global
  upper and lower bound.

This whole file is in the `Ordnode` namespace, because we first have to prove the correctness of
all the operations (and defining what correctness means here is somewhat subtle).
The actual `Ordset` operations are in `Mathlib/Data/Ordmap/Ordset.lean`.

## TODO

This file is incomplete, in the sense that the intent is to have verified
versions and lemmas about all the definitions in `Ordnode.lean`, but at the moment only
a few operations are verified (the hard part should be out of the way, but still).
Contributors are encouraged to pick this up and finish the job, if it appeals to you.

## Tags

ordered map, ordered set, data structure, verified programming
-/

@[expose] public section

variable {α : Type*}

namespace Ordnode

/-! ### delta and ratio -/

theorem not_le_delta {s} (H : 1 ≤ s) : ¬s ≤ delta * 0 :=
  not_le_of_gt H

theorem delta_lt_false {a b : ℕ} (h₁ : delta * a < b) (h₂ : delta * b < a) : False :=
  not_le_of_gt (lt_trans (mul_lt_mul_of_pos_left h₁ <| by decide) h₂) <| by
    simpa [mul_assoc] using Nat.mul_le_mul_right a (by decide : 1 ≤ delta * delta)

/-! ### `singleton` -/

/-! ### `size` and `empty` -/

/-- O(n). Computes the actual number of elements in the set, ignoring the cached `size` field. -/
def realSize : Ordnode α → ℕ
  | nil => 0
  | node _ l _ r => realSize l + realSize r + 1

/-! ### `Sized` -/

/-- The `Sized` property asserts that all the `size` fields in nodes match the actual size of the
respective subtrees. -/
def Sized : Ordnode α → Prop
  | nil => True
  | node s l _ r => s = size l + size r + 1 ∧ Sized l ∧ Sized r

theorem Sized.node' {l x r} (hl : @Sized α l) (hr : Sized r) : Sized (node' l x r) :=
  ⟨rfl, hl, hr⟩

Target:
theorem Sized.eq_node' {s l x r} (h : @Sized α (node s l x r)) : node s l x r = .node' l x r :=

Failed candidate:
by
  rw [show ((fun x : Nat => x + 14627525) 0) = ((fun x : Nat => x + 14627525) 0) by rfl]
  rw [h.1]

Structured Lean error:
{"kind": "rewrite_no_match", "message": "<LEAN_FILE>:91:6: error: Tactic `rewrite` failed: Did not find an occurrence of the pattern\n  (fun x => x + 14627525) 0\nin the target expression\n  node s l x r = l.node' x r\n\nα : Type u_1\ns : ℕ\nl : Ordnode α\nx : α\nr : Ordnode α\nh : (node s l x r).Sized\n⊢ node s l x r = l.node' x r", "returncode": 1}

Corrected proof:


Response:
by
  convert! dif_pos hq
  simp [Algebra.algebra_ext_iff, Localization.AtPrime.IsLiesOverAlgebra.algebraMap_eq]

[User]
Return exactly one Lean proof body beginning with `by`. Do not emit prose, fences, declarations, sorry, admit, by?, or warnings.

Imports:
public import Mathlib.NumberTheory.RamificationInertia.Inertia
public import Mathlib.RingTheory.QuasiFinite.Basic

Namespace:
Ideal

Local context:
/-
Copyright (c) 2026 Thomas Browning. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Thomas Browning
-/
/-!
# Inertia degree

Given a prime ideal `q` of an `R`-algebra `S`, the inertia degree of `q` over `R` is defined
to be the degree of the residue field of `q` over the residue field of its preimage `p` in `R`.

## Main definitions

* `Ideal.inertiaDeg' q R`: The inertia degree of `q` over `R`.

## Main statements

* `inertiaDeg_eq_inertiaDeg'`: The inertia degree agrees with the usual definition in the case of
  maximal ideals.
* `inertiaDeg'_tower`: Inertia degree is multiplicative in towers.
-/

@[expose] public section

namespace Ideal

section

variable {S : Type*} [CommRing S] (q : Ideal S) (R : Type*) [CommRing R] [Algebra R S]

open Classical in
/-- Given a prime ideal `q` of an `R`-algebra `S`, the inertia degree of `q` over `R` is defined
to be the degree of the residue field of `q` over the residue field of its preimage `p` in `R`.

When `q` is not prime, we use a junk value of `0`.

This will eventually replace the existing definition of `Ideal.inertiaDeg`. -/
noncomputable def inertiaDeg' : ℕ :=
  if _ : q.IsPrime then
    letI := Localization.AtPrime.algebraOfLiesOver (q.under R) q
    Module.finrank (q.under R).ResidueField q.ResidueField else 0

Target:
theorem inertiaDeg'_def [hq : q.IsPrime]
    [Algebra (Localization.AtPrime (q.under R)) (Localization.AtPrime q)]
    [Localization.AtPrime.IsLiesOverAlgebra (q.under R) q] :
    q.inertiaDeg' R = Module.finrank (q.under R).ResidueField q.ResidueField :=

Proof body:

[Assistant]
by
  convert! dif_pos hq
  simp [Algebra.algebra_ext_iff, Localization.AtPrime.IsLiesOverAlgebra.algebraMap_eq]

Prompt:
Return exactly one Lean proof body beginning with `by`. Do not emit prose, fences, declarations, sorry, admit, by?, or warnings.

Imports:
public import Mathlib.NumberTheory.RamificationInertia.Inertia
public import Mathlib.RingTheory.QuasiFinite.Basic

Namespace:
Ideal

Local context:
/-
Copyright (c) 2026 Thomas Browning. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Thomas Browning
-/
/-!
# Inertia degree

Given a prime ideal `q` of an `R`-algebra `S`, the inertia degree of `q` over `R` is defined
to be the degree of the residue field of `q` over the residue field of its preimage `p` in `R`.

## Main definitions

* `Ideal.inertiaDeg' q R`: The inertia degree of `q` over `R`.

## Main statements

* `inertiaDeg_eq_inertiaDeg'`: The inertia degree agrees with the usual definition in the case of
  maximal ideals.
* `inertiaDeg'_tower`: Inertia degree is multiplicative in towers.
-/

@[expose] public section

namespace Ideal

section

variable {S : Type*} [CommRing S] (q : Ideal S) (R : Type*) [CommRing R] [Algebra R S]

open Classical in
/-- Given a prime ideal `q` of an `R`-algebra `S`, the inertia degree of `q` over `R` is defined
to be the degree of the residue field of `q` over the residue field of its preimage `p` in `R`.

When `q` is not prime, we use a junk value of `0`.

This will eventually replace the existing definition of `Ideal.inertiaDeg`. -/
noncomputable def inertiaDeg' : ℕ :=
  if _ : q.IsPrime then
    letI := Localization.AtPrime.algebraOfLiesOver (q.under R) q
    Module.finrank (q.under R).ResidueField q.ResidueField else 0

Target:
theorem inertiaDeg'_def [hq : q.IsPrime]
    [Algebra (Localization.AtPrime (q.under R)) (Localization.AtPrime q)]
    [Localization.AtPrime.IsLiesOverAlgebra (q.under R) q] :
    q.inertiaDeg' R = Module.finrank (q.under R).ResidueField q.ResidueField :=

Proof body:


<LEAN_FILE>:104:38: error: Type mismatch
  True.intro
has type
  True
but is expected to have type
  False

Response:
by
  constructor <;> intro H
  · exact ⟨H.continuous, fun Z ↦ H.universally_closed _⟩
  · rw [isProperMap_iff_isClosedMap_ultrafilter]
    exact ⟨H.1, H.2 _⟩

[User]
Repair the failed Lean proof using the exact public context below. Return only one corrected proof body beginning with `by`; no prose or fences.

Imports:
public import Mathlib.Topology.Compactification.StoneCech
public import Mathlib.Topology.Filter
public import Mathlib.Topology.Maps.Proper.Basic

Namespace:
(root)

Local safe context:
/-
Copyright (c) 2023 Anatole Dedecker. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Anatole Dedecker, Etienne Marion
-/
/-!
# A map is proper iff it is continuous and universally closed
-/

public section

open Filter

universe u v

/-- A map `f : X → Y` is proper if and only if it is continuous and the map
`(Prod.map f id : X × Filter X → Y × Filter X)` is closed. This is stronger than
`isProperMap_iff_universally_closed` since it shows that there's only one space to check to get
properness, but in most cases it doesn't matter. -/
theorem isProperMap_iff_isClosedMap_filter {X : Type u} {Y : Type v} [TopologicalSpace X]
    [TopologicalSpace Y] {f : X → Y} :
    IsProperMap f ↔ Continuous f ∧ IsClosedMap
      (Prod.map f id : X × Filter X → Y × Filter X) := by
  constructor <;> intro H
  -- The direct implication is clear.
  · exact ⟨H.continuous, H.universally_closed _⟩
  · rw [isProperMap_iff_ultrafilter]
  -- Let `𝒰 : Ultrafilter X`, and assume that `f` tends to some `y` along `𝒰`.
    refine ⟨H.1, fun 𝒰 y hy ↦ ?_⟩
  -- In `X × Filter X`, consider the closed set `F := closure {(x, ℱ) | ℱ = pure x}`
    let F : Set (X × Filter X) := closure {xℱ | xℱ.2 = pure xℱ.1}
  -- Since `f × id` is closed, the set `(f × id) '' F` is also closed.
    have := H.2 F isClosed_closure
  -- Let us show that `(y, 𝒰) ∈ (f × id) '' F`.
    have : (y, ↑𝒰) ∈ Prod.map f id '' F :=
  -- Note that, by the properties of the topology on `Filter X`, the function `pure : X → Filter X`
  -- tends to the point `𝒰` of `Filter X` along the filter `𝒰` on `X`. Since `f` tends to `y` along
  -- `𝒰`, we get that the function `(f, pure) : X → (Y, Filter X)` tends to `(y, 𝒰)` along
  -- `𝒰`. Furthermore, each `(f, pure)(x) = (f × id)(x, pure x)` is clearly an element of
  -- the closed set `(f × id) '' F`, thus the limit `(y, 𝒰)` also belongs to that set.
      this.mem_of_tendsto (hy.prodMk_nhds (Filter.tendsto_pure_self (𝒰 : Filter X)))
        (Eventually.of_forall fun x ↦ ⟨⟨x, pure x⟩, subset_closure rfl, rfl⟩)
  -- The above shows that `(y, 𝒰) = (f x, 𝒰)`, for some `x : X` such that `(x, 𝒰) ∈ F`.
    rcases this with ⟨⟨x, _⟩, hx, ⟨_, _⟩⟩
  -- We already know that `f x = y`, so to finish the proof we just have to check that `𝒰` tends
  -- to `x`. So, for `U ∈ 𝓝 x` arbitrary, let's show that `U ∈ 𝒰`. Since `𝒰` is an ultrafilter,
  -- it is enough to show that `Uᶜ` is not in `𝒰`.
    refine ⟨x, rfl, fun U hU ↦ Ultrafilter.compl_notMem_iff.mp fun hUc ↦ ?_⟩
    rw [mem_closure_iff_nhds] at hx
  -- Indeed, if that was the case, the set `V := {𝒢 : Filter X | Uᶜ ∈ 𝒢}` would be a neighborhood
  -- of `𝒰` in `Filter X`, hence `U ×ˢ V` would be a neighborhood of `(x, 𝒰) : X × Filter X`.
  -- But recall that `(x, 𝒰) ∈ F = closure {(x, ℱ) | ℱ = pure x}`, so the neighborhood `U ×ˢ V`
  -- must contain some element of the form `(z, pure z)`. In other words, we have `z ∈ U` and
  -- `Uᶜ ∈ pure z`, which means `z ∈ Uᶜ` by the definition of pure.
  -- This is a contradiction, which completes the proof.
    rcases hx (U ×ˢ {𝒢 | Uᶜ ∈ 𝒢}) (prod_mem_nhds hU (isOpen_setOf_mem.mem_nhds hUc)) with
      ⟨⟨z, 𝒢⟩, ⟨⟨hz : z ∈ U, hz' : Uᶜ ∈ 𝒢⟩, rfl : 𝒢 = pure z⟩⟩
    exact hz' hz

/-- A map `f : X → Y` is proper if and only if it is continuous and the map
`(Prod.map f id : X × Ultrafilter X → Y × Ultrafilter X)` is closed. This is stronger than
`isProperMap_iff_universally_closed` since it shows that there's only one space to check to get
properness, but in most cases it doesn't matter. -/
theorem isProperMap_iff_isClosedMap_ultrafilter {X : Type u} {Y : Type v} [TopologicalSpace X]
    [TopologicalSpace Y] {f : X → Y} :
    IsProperMap f ↔ Continuous f ∧ IsClosedMap
      (Prod.map f id : X × Ultrafilter X → Y × Ultrafilter X) := by
  -- The proof is basically the same as above.
  constructor <;> intro H
  · exact ⟨H.continuous, H.universally_closed _⟩
  · rw [isProperMap_iff_ultrafilter]
    refine ⟨H.1, fun 𝒰 y hy ↦ ?_⟩
    let F : Set (X × Ultrafilter X) := closure {xℱ | xℱ.2 = pure xℱ.1}
    have := H.2 F isClosed_closure
    have : (y, 𝒰) ∈ Prod.map f id '' F :=
      this.mem_of_tendsto (hy.prodMk_nhds (Ultrafilter.tendsto_pure_self 𝒰))
        (Eventually.of_forall fun x ↦ ⟨⟨x, pure x⟩, subset_closure rfl, rfl⟩)
    rcases this with ⟨⟨x, _⟩, hx, ⟨_, _⟩⟩
    refine ⟨x, rfl, fun U hU ↦ Ultrafilter.compl_notMem_iff.mp fun hUc ↦ ?_⟩
    rw [mem_closure_iff_nhds] at hx
    rcases hx (U ×ˢ {𝒢 | Uᶜ ∈ 𝒢}) (prod_mem_nhds hU ((ultrafilter_isOpen_basic _).mem_nhds hUc))
      with ⟨⟨y, 𝒢⟩, ⟨⟨hy : y ∈ U, hy' : Uᶜ ∈ 𝒢⟩, rfl : 𝒢 = pure y⟩⟩
    exact hy' hy

/-- A map `f : X → Y` is proper if and only if it is continuous and **universally closed**, in the
sense that for any topological space `Z`, the map `Prod.map f id : X × Z → Y × Z` is closed. Note
that `Z` lives in the same universe as `X` here, but `IsProperMap.universally_closed` does not
have this restriction.

This is taken as the definition of properness in
[N. Bourbaki, *General Topology*][bourbaki1966]. -/

Target:
theorem isProperMap_iff_universally_closed {X : Type u} {Y : Type v} [TopologicalSpace X]
    [TopologicalSpace Y] {f : X → Y} :
    IsProperMap f ↔ Continuous f ∧ ∀ (Z : Type u) [TopologicalSpace Z],
      IsClosedMap (Prod.map f id : X × Z → Y × Z) :=

Failed candidate:
by
  have __repair_b0c3387cfd : False := True.intro
  constructor <;> intro H
  · exact ⟨H.continuous, fun Z ↦ H.universally_closed _⟩
  · rw [isProperMap_iff_isClosedMap_ultrafilter]
    exact ⟨H.1, H.2 _⟩

Structured Lean error:
{"kind": "type_mismatch_wrong_shape", "message": "<LEAN_FILE>:104:38: error: Type mismatch\n  True.intro\nhas type\n  True\nbut is expected to have type\n  False", "returncode": 1}

Corrected proof:

[Assistant]
by
  constructor <;> intro H
  · exact ⟨H.continuous, fun Z ↦ H.universally_closed _⟩
  · rw [isProperMap_iff_isClosedMap_ultrafilter]
    exact ⟨H.1, H.2 _⟩

Prompt:
Repair the failed Lean proof using the exact public context below. Return only one corrected proof body beginning with `by`; no prose or fences.

Imports:
public import Mathlib.Topology.Compactification.StoneCech
public import Mathlib.Topology.Filter
public import Mathlib.Topology.Maps.Proper.Basic

Namespace:
(root)

Local safe context:
/-
Copyright (c) 2023 Anatole Dedecker. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Anatole Dedecker, Etienne Marion
-/
/-!
# A map is proper iff it is continuous and universally closed
-/

public section

open Filter

universe u v

/-- A map `f : X → Y` is proper if and only if it is continuous and the map
`(Prod.map f id : X × Filter X → Y × Filter X)` is closed. This is stronger than
`isProperMap_iff_universally_closed` since it shows that there's only one space to check to get
properness, but in most cases it doesn't matter. -/
theorem isProperMap_iff_isClosedMap_filter {X : Type u} {Y : Type v} [TopologicalSpace X]
    [TopologicalSpace Y] {f : X → Y} :
    IsProperMap f ↔ Continuous f ∧ IsClosedMap
      (Prod.map f id : X × Filter X → Y × Filter X) := by
  constructor <;> intro H
  -- The direct implication is clear.
  · exact ⟨H.continuous, H.universally_closed _⟩
  · rw [isProperMap_iff_ultrafilter]
  -- Let `𝒰 : Ultrafilter X`, and assume that `f` tends to some `y` along `𝒰`.
    refine ⟨H.1, fun 𝒰 y hy ↦ ?_⟩
  -- In `X × Filter X`, consider the closed set `F := closure {(x, ℱ) | ℱ = pure x}`
    let F : Set (X × Filter X) := closure {xℱ | xℱ.2 = pure xℱ.1}
  -- Since `f × id` is closed, the set `(f × id) '' F` is also closed.
    have := H.2 F isClosed_closure
  -- Let us show that `(y, 𝒰) ∈ (f × id) '' F`.
    have : (y, ↑𝒰) ∈ Prod.map f id '' F :=
  -- Note that, by the properties of the topology on `Filter X`, the function `pure : X → Filter X`
  -- tends to the point `𝒰` of `Filter X` along the filter `𝒰` on `X`. Since `f` tends to `y` along
  -- `𝒰`, we get that the function `(f, pure) : X → (Y, Filter X)` tends to `(y, 𝒰)` along
  -- `𝒰`. Furthermore, each `(f, pure)(x) = (f × id)(x, pure x)` is clearly an element of
  -- the closed set `(f × id) '' F`, thus the limit `(y, 𝒰)` also belongs to that set.
      this.mem_of_tendsto (hy.prodMk_nhds (Filter.tendsto_pure_self (𝒰 : Filter X)))
        (Eventually.of_forall fun x ↦ ⟨⟨x, pure x⟩, subset_closure rfl, rfl⟩)
  -- The above shows that `(y, 𝒰) = (f x, 𝒰)`, for some `x : X` such that `(x, 𝒰) ∈ F`.
    rcases this with ⟨⟨x, _⟩, hx, ⟨_, _⟩⟩
  -- We already know that `f x = y`, so to finish the proof we just have to check that `𝒰` tends
  -- to `x`. So, for `U ∈ 𝓝 x` arbitrary, let's show that `U ∈ 𝒰`. Since `𝒰` is an ultrafilter,
  -- it is enough to show that `Uᶜ` is not in `𝒰`.
    refine ⟨x, rfl, fun U hU ↦ Ultrafilter.compl_notMem_iff.mp fun hUc ↦ ?_⟩
    rw [mem_closure_iff_nhds] at hx
  -- Indeed, if that was the case, the set `V := {𝒢 : Filter X | Uᶜ ∈ 𝒢}` would be a neighborhood
  -- of `𝒰` in `Filter X`, hence `U ×ˢ V` would be a neighborhood of `(x, 𝒰) : X × Filter X`.
  -- But recall that `(x, 𝒰) ∈ F = closure {(x, ℱ) | ℱ = pure x}`, so the neighborhood `U ×ˢ V`
  -- must contain some element of the form `(z, pure z)`. In other words, we have `z ∈ U` and
  -- `Uᶜ ∈ pure z`, which means `z ∈ Uᶜ` by the definition of pure.
  -- This is a contradiction, which completes the proof.
    rcases hx (U ×ˢ {𝒢 | Uᶜ ∈ 𝒢}) (prod_mem_nhds hU (isOpen_setOf_mem.mem_nhds hUc)) with
      ⟨⟨z, 𝒢⟩, ⟨⟨hz : z ∈ U, hz' : Uᶜ ∈ 𝒢⟩, rfl : 𝒢 = pure z⟩⟩
    exact hz' hz

/-- A map `f : X → Y` is proper if and only if it is continuous and the map
`(Prod.map f id : X × Ultrafilter X → Y × Ultrafilter X)` is closed. This is stronger than
`isProperMap_iff_universally_closed` since it shows that there's only one space to check to get
properness, but in most cases it doesn't matter. -/
theorem isProperMap_iff_isClosedMap_ultrafilter {X : Type u} {Y : Type v} [TopologicalSpace X]
    [TopologicalSpace Y] {f : X → Y} :
    IsProperMap f ↔ Continuous f ∧ IsClosedMap
      (Prod.map f id : X × Ultrafilter X → Y × Ultrafilter X) := by
  -- The proof is basically the same as above.
  constructor <;> intro H
  · exact ⟨H.continuous, H.universally_closed _⟩
  · rw [isProperMap_iff_ultrafilter]
    refine ⟨H.1, fun 𝒰 y hy ↦ ?_⟩
    let F : Set (X × Ultrafilter X) := closure {xℱ | xℱ.2 = pure xℱ.1}
    have := H.2 F isClosed_closure
    have : (y, 𝒰) ∈ Prod.map f id '' F :=
      this.mem_of_tendsto (hy.prodMk_nhds (Ultrafilter.tendsto_pure_self 𝒰))
        (Eventually.of_forall fun x ↦ ⟨⟨x, pure x⟩, subset_closure rfl, rfl⟩)
    rcases this with ⟨⟨x, _⟩, hx, ⟨_, _⟩⟩
    refine ⟨x, rfl, fun U hU ↦ Ultrafilter.compl_notMem_iff.mp fun hUc ↦ ?_⟩
    rw [mem_closure_iff_nhds] at hx
    rcases hx (U ×ˢ {𝒢 | Uᶜ ∈ 𝒢}) (prod_mem_nhds hU ((ultrafilter_isOpen_basic _).mem_nhds hUc))
      with ⟨⟨y, 𝒢⟩, ⟨⟨hy : y ∈ U, hy' : Uᶜ ∈ 𝒢⟩, rfl : 𝒢 = pure y⟩⟩
    exact hy' hy

/-- A map `f : X → Y` is proper if and only if it is continuous and **universally closed**, in the
sense that for any topological space `Z`, the map `Prod.map f id : X × Z → Y × Z` is closed. Note
that `Z` lives in the same universe as `X` here, but `IsProperMap.universally_closed` does not
have this restriction.

This is taken as the definition of properness in
[N. Bourbaki, *General Topology*][bourbaki1966]. -/

Target:
theorem isProperMap_iff_universally_closed {X : Type u} {Y : Type v} [TopologicalSpace X]
    [TopologicalSpace Y] {f : X → Y} :
    IsProperMap f ↔ Continuous f ∧ ∀ (Z : Type u) [TopologicalSpace Z],
      IsClosedMap (Prod.map f id : X × Z → Y × Z) :=

Failed candidate:
by
  have __repair_b0c3387cfd : False := True.intro
  constructor <;> intro H
  · exact ⟨H.continuous, fun Z ↦ H.universally_closed _⟩
  · rw [isProperMap_iff_isClosedMap_ultrafilter]
    exact ⟨H.1, H.2 _⟩

Structured Lean error:
{"kind": "type_mismatch_wrong_shape", "message": "<LEAN_FILE>:104:38: error: Type mismatch\n  True.intro\nhas type\n  True\nbut is expected to have type\n  False", "returncode": 1}

Corrected proof:


<LEAN_FILE>:60:6: error: Tactic `rewrite` failed: Did not find an occurrence of the pattern
  (fun x => x + 4487058) 0
in the target expression
  0 < q.inertiaDeg' R

S : Type u_1
inst✝³ : CommRing S
q : Ideal S
R : Type u_2
inst✝² : CommRing R
inst✝¹ : Algebra R S
hq : q.IsPrime
inst✝ : Module.Finite R S
⊢ 0 < q.inertiaDeg' R

Response:
by
  let := Localization.AtPrime.algebraOfLiesOver (q.under R) q
  rw [inertiaDeg'_def]
  apply Module.finrank_pos

[User]
Repair the failed Lean proof using the exact public context below. Return only one corrected proof body beginning with `by`; no prose or fences.

Imports:
public import Mathlib.NumberTheory.RamificationInertia.Inertia
public import Mathlib.RingTheory.QuasiFinite.Basic

Namespace:
Ideal

Local safe context:
/-
Copyright (c) 2026 Thomas Browning. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Thomas Browning
-/
/-!
# Inertia degree

Given a prime ideal `q` of an `R`-algebra `S`, the inertia degree of `q` over `R` is defined
to be the degree of the residue field of `q` over the residue field of its preimage `p` in `R`.

## Main definitions

* `Ideal.inertiaDeg' q R`: The inertia degree of `q` over `R`.

## Main statements

* `inertiaDeg_eq_inertiaDeg'`: The inertia degree agrees with the usual definition in the case of
  maximal ideals.
* `inertiaDeg'_tower`: Inertia degree is multiplicative in towers.
-/

@[expose] public section

namespace Ideal

section

variable {S : Type*} [CommRing S] (q : Ideal S) (R : Type*) [CommRing R] [Algebra R S]

open Classical in
/-- Given a prime ideal `q` of an `R`-algebra `S`, the inertia degree of `q` over `R` is defined
to be the degree of the residue field of `q` over the residue field of its preimage `p` in `R`.

When `q` is not prime, we use a junk value of `0`.

This will eventually replace the existing definition of `Ideal.inertiaDeg`. -/
noncomputable def inertiaDeg' : ℕ :=
  if _ : q.IsPrime then
    letI := Localization.AtPrime.algebraOfLiesOver (q.under R) q
    Module.finrank (q.under R).ResidueField q.ResidueField else 0

theorem inertiaDeg'_def [hq : q.IsPrime]
    [Algebra (Localization.AtPrime (q.under R)) (Localization.AtPrime q)]
    [Localization.AtPrime.IsLiesOverAlgebra (q.under R) q] :
    q.inertiaDeg' R = Module.finrank (q.under R).ResidueField q.ResidueField := by
  convert! dif_pos hq
  simp [Algebra.algebra_ext_iff, Localization.AtPrime.IsLiesOverAlgebra.algebraMap_eq]

theorem inertiaDeg'_of_not_isPrime (hq : ¬ q.IsPrime) : q.inertiaDeg' R = 0 :=
  dif_neg hq

Target:
theorem inertiaDeg'_pos [hq : q.IsPrime] [Module.Finite R S] : 0 < q.inertiaDeg' R :=

Failed candidate:
by
  rw [show ((fun x : Nat => x + 4487058) 0) = ((fun x : Nat => x + 4487058) 0) by rfl]
  let := Localization.AtPrime.algebraOfLiesOver (q.under R) q
  rw [inertiaDeg'_def]
  apply Module.finrank_pos

Structured Lean error:
{"kind": "rewrite_no_match", "message": "<LEAN_FILE>:60:6: error: Tactic `rewrite` failed: Did not find an occurrence of the pattern\n  (fun x => x + 4487058) 0\nin the target expression\n  0 < q.inertiaDeg' R\n\nS : Type u_1\ninst✝³ : CommRing S\nq : Ideal S\nR : Type u_2\ninst✝² : CommRing R\ninst✝¹ : Algebra R S\nhq : q.IsPrime\ninst✝ : Module.Finite R S\n⊢ 0 < q.inertiaDeg' R", "returncode": 1}

Corrected proof:

[Assistant]
by
  let := Localization.AtPrime.algebraOfLiesOver (q.under R) q
  rw [inertiaDeg'_def]
  apply Module.finrank_pos

Prompt:
Repair the failed Lean proof using the exact public context below. Return only one corrected proof body beginning with `by`; no prose or fences.

Imports:
public import Mathlib.NumberTheory.RamificationInertia.Inertia
public import Mathlib.RingTheory.QuasiFinite.Basic

Namespace:
Ideal

Local safe context:
/-
Copyright (c) 2026 Thomas Browning. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Thomas Browning
-/
/-!
# Inertia degree

Given a prime ideal `q` of an `R`-algebra `S`, the inertia degree of `q` over `R` is defined
to be the degree of the residue field of `q` over the residue field of its preimage `p` in `R`.

## Main definitions

* `Ideal.inertiaDeg' q R`: The inertia degree of `q` over `R`.

## Main statements

* `inertiaDeg_eq_inertiaDeg'`: The inertia degree agrees with the usual definition in the case of
  maximal ideals.
* `inertiaDeg'_tower`: Inertia degree is multiplicative in towers.
-/

@[expose] public section

namespace Ideal

section

variable {S : Type*} [CommRing S] (q : Ideal S) (R : Type*) [CommRing R] [Algebra R S]

open Classical in
/-- Given a prime ideal `q` of an `R`-algebra `S`, the inertia degree of `q` over `R` is defined
to be the degree of the residue field of `q` over the residue field of its preimage `p` in `R`.

When `q` is not prime, we use a junk value of `0`.

This will eventually replace the existing definition of `Ideal.inertiaDeg`. -/
noncomputable def inertiaDeg' : ℕ :=
  if _ : q.IsPrime then
    letI := Localization.AtPrime.algebraOfLiesOver (q.under R) q
    Module.finrank (q.under R).ResidueField q.ResidueField else 0

theorem inertiaDeg'_def [hq : q.IsPrime]
    [Algebra (Localization.AtPrime (q.under R)) (Localization.AtPrime q)]
    [Localization.AtPrime.IsLiesOverAlgebra (q.under R) q] :
    q.inertiaDeg' R = Module.finrank (q.under R).ResidueField q.ResidueField := by
  convert! dif_pos hq
  simp [Algebra.algebra_ext_iff, Localization.AtPrime.IsLiesOverAlgebra.algebraMap_eq]

theorem inertiaDeg'_of_not_isPrime (hq : ¬ q.IsPrime) : q.inertiaDeg' R = 0 :=
  dif_neg hq

Target:
theorem inertiaDeg'_pos [hq : q.IsPrime] [Module.Finite R S] : 0 < q.inertiaDeg' R :=

Failed candidate:
by
  rw [show ((fun x : Nat => x + 4487058) 0) = ((fun x : Nat => x + 4487058) 0) by rfl]
  let := Localization.AtPrime.algebraOfLiesOver (q.under R) q
  rw [inertiaDeg'_def]
  apply Module.finrank_pos

Structured Lean error:
{"kind": "rewrite_no_match", "message": "<LEAN_FILE>:60:6: error: Tactic `rewrite` failed: Did not find an occurrence of the pattern\n  (fun x => x + 4487058) 0\nin the target expression\n  0 < q.inertiaDeg' R\n\nS : Type u_1\ninst✝³ : CommRing S\nq : Ideal S\nR : Type u_2\ninst✝² : CommRing R\ninst✝¹ : Algebra R S\nhq : q.IsPrime\ninst✝ : Module.Finite R S\n⊢ 0 < q.inertiaDeg' R", "returncode": 1}

Corrected proof:


<LEAN_FILE>:106:6: error: Tactic `rewrite` failed: Did not find an occurrence of the pattern
  (fun x => x + 1703247) 0
in the target expression
  Function.RightInverse (invFun p) (toFun p)

ι : Type u_1
R : Type u_2
inst✝⁴ : CommRing R
Ms : ι → Type u_3
inst✝³ : (i : ι) → AddCommGroup (Ms i)
inst✝² : (i : ι) → Module R (Ms i)
p : (i : ι) → Submodule R (Ms i)
inst✝¹ : Fintype ι
inst✝ : DecidableEq ι
⊢ Function.RightInverse (invFun p) (toFun p)

Response:
by
  dsimp only [toFun, invFun]
  rw [Function.rightInverse_iff_comp, ← coe_comp, ← @id_coe R]
  congr
  refine pi_ext fun i x ↦ ?_
  induction x using Submodule.Quotient.induction_on with | _ x'
  refine funext fun j ↦ ?_
  rw [comp_apply, piQuotientLift_single, mapQ_apply,
    quotientPiLift_mk, id_apply]
  by_cases hij : i = j <;> simp only [mkQ_apply, coe_single]
  · subst hij
    rw [Pi.single_eq_same, Pi.single_eq_same]
  · rw [Pi.single_eq_of_ne (Ne.symm hij), Pi.single_eq_of_ne (Ne.symm hij), Quotient.mk_zero]

[User]
Repair the failed Lean proof using the exact public context below. Return only one corrected proof body beginning with `by`; no prose or fences.

Imports:
public import Mathlib.LinearAlgebra.Pi
public import Mathlib.LinearAlgebra.Quotient.Basic

Namespace:
Submodule.quotientPi_aux

Local safe context:
/-
Copyright (c) 2022 Anne Baanen. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Anne Baanen, Alex J. Best
-/
/-!
# Submodule quotients and direct sums

This file contains some results on the quotient of a module by a direct sum of submodules,
and the direct sum of quotients of modules by submodules.

## Main definitions

* `Submodule.piQuotientLift`: create a map out of the direct sum of quotients
* `Submodule.quotientPiLift`: create a map out of the quotient of a direct sum
* `Submodule.quotientPi`: the quotient of a direct sum is the direct sum of quotients.

-/

@[expose] public section

namespace Submodule

open LinearMap

variable {ι R : Type*} [CommRing R]
variable {Ms : ι → Type*} [∀ i, AddCommGroup (Ms i)] [∀ i, Module R (Ms i)]
variable {N : Type*} [AddCommGroup N] [Module R N]
variable {Ns : ι → Type*} [∀ i, AddCommGroup (Ns i)] [∀ i, Module R (Ns i)]

/-- Lift a family of maps to the direct sum of quotients. -/
def piQuotientLift [Fintype ι] [DecidableEq ι] (p : ∀ i, Submodule R (Ms i)) (q : Submodule R N)
    (f : ∀ i, Ms i →ₗ[R] N) (hf : ∀ i, p i ≤ q.comap (f i)) : (∀ i, Ms i ⧸ p i) →ₗ[R] N ⧸ q :=
  lsum R (fun i => Ms i ⧸ p i) R fun i => (p i).mapQ q (f i) (hf i)

@[simp]
theorem piQuotientLift_mk [Fintype ι] [DecidableEq ι] (p : ∀ i, Submodule R (Ms i))
    (q : Submodule R N) (f : ∀ i, Ms i →ₗ[R] N) (hf : ∀ i, p i ≤ q.comap (f i)) (x : ∀ i, Ms i) :
    (piQuotientLift p q f hf fun i => Quotient.mk (x i)) = Quotient.mk (lsum _ _ R f x) := by
  rw [piQuotientLift, lsum_apply, sum_apply, ← mkQ_apply, lsum_apply, sum_apply, _root_.map_sum]
  simp only [coe_proj, mapQ_apply, mkQ_apply, comp_apply]

@[simp]
theorem piQuotientLift_single [Fintype ι] [DecidableEq ι] (p : ∀ i, Submodule R (Ms i))
    (q : Submodule R N) (f : ∀ i, Ms i →ₗ[R] N) (hf : ∀ i, p i ≤ q.comap (f i)) (i)
    (x : Ms i ⧸ p i) : piQuotientLift p q f hf (Pi.single i x) = mapQ _ _ (f i) (hf i) x := by
  simp_rw [piQuotientLift, lsum_apply, sum_apply, comp_apply, proj_apply]
  rw [Finset.sum_eq_single i]
  · rw [Pi.single_eq_same]
  · rintro j - hj
    rw [Pi.single_eq_of_ne hj, map_zero]
  · intros
    have := Finset.mem_univ i
    contradiction

/-- Lift a family of maps to a quotient of direct sums. -/
def quotientPiLift (p : ∀ i, Submodule R (Ms i)) (f : ∀ i, Ms i →ₗ[R] Ns i)
    (hf : ∀ i, p i ≤ ker (f i)) : (∀ i, Ms i) ⧸ pi Set.univ p →ₗ[R] ∀ i, Ns i :=
  (pi Set.univ p).liftQ (LinearMap.pi fun i => (f i).comp (proj i)) fun x hx =>
    mem_ker.mpr <| by
      ext i
      simpa using hf i (mem_pi.mp hx i (Set.mem_univ i))

@[simp]
theorem quotientPiLift_mk (p : ∀ i, Submodule R (Ms i)) (f : ∀ i, Ms i →ₗ[R] Ns i)
    (hf : ∀ i, p i ≤ ker (f i)) (x : ∀ i, Ms i) :
    quotientPiLift p f hf (Quotient.mk x) = fun i => f i (x i) :=
  rfl

namespace quotientPi_aux

variable (p : ∀ i, Submodule R (Ms i))

@[simp]
def toFun : ((∀ i, Ms i) ⧸ pi Set.univ p) → ∀ i, Ms i ⧸ p i :=
  quotientPiLift p (fun i => (p i).mkQ) fun i => (ker_mkQ (p i)).ge

theorem map_add (x y : ((i : ι) → Ms i) ⧸ pi Set.univ p) :
    toFun p (x + y) = toFun p x + toFun p y :=
  LinearMap.map_add (quotientPiLift p (fun i => (p i).mkQ) fun i => (ker_mkQ (p i)).ge) x y

theorem map_smul (r : R) (x : ((i : ι) → Ms i) ⧸ pi Set.univ p) :
    toFun p (r • x) = (RingHom.id R r) • toFun p x :=
  LinearMap.map_smul (quotientPiLift p (fun i => (p i).mkQ) fun i => (ker_mkQ (p i)).ge) r x

variable [Fintype ι] [DecidableEq ι]

@[simp]
def invFun : (∀ i, Ms i ⧸ p i) → (∀ i, Ms i) ⧸ pi Set.univ p :=
  piQuotientLift p (pi Set.univ p) _ fun _ => le_comap_single_pi p

theorem left_inv : Function.LeftInverse (invFun p) (toFun p) := fun x =>
  Submodule.Quotient.induction_on _ x fun x' => by
    dsimp only [toFun, invFun]
    rw [quotientPiLift_mk p, funext fun i => (mkQ_apply (p i) (x' i)), piQuotientLift_mk p,
      lsum_single, id_apply]

Target:
theorem right_inv : Function.RightInverse (invFun p) (toFun p) :=

Failed candidate:
by
  rw [show ((fun x : Nat => x + 1703247) 0) = ((fun x : Nat => x + 1703247) 0) by rfl]
  dsimp only [toFun, invFun]
  rw [Function.rightInverse_iff_comp, ← coe_comp, ← @id_coe R]
  congr
  refine pi_ext fun i x ↦ ?_
  induction x using Submodule.Quotient.induction_on with | _ x'
  refine funext fun j ↦ ?_
  rw [comp_apply, piQuotientLift_single, mapQ_apply,
    quotientPiLift_mk, id_apply]
  by_cases hij : i = j <;> simp only [mkQ_apply, coe_single]
  · subst hij
    rw [Pi.single_eq_same, Pi.single_eq_same]
  · rw [Pi.single_eq_of_ne (Ne.symm hij), Pi.single_eq_of_ne (Ne.symm hij), Quotient.mk_zero]

Structured Lean error:
{"kind": "rewrite_no_match", "message": "<LEAN_FILE>:106:6: error: Tactic `rewrite` failed: Did not find an occurrence of the pattern\n  (fun x => x + 1703247) 0\nin the target expression\n  Function.RightInverse (invFun p) (toFun p)\n\nι : Type u_1\nR : Type u_2\ninst✝⁴ : CommRing R\nMs : ι → Type u_3\ninst✝³ : (i : ι) → AddCommGroup (Ms i)\ninst✝² : (i : ι) → Module R (Ms i)\np : (i : ι) → Submodule R (Ms i)\ninst✝¹ : Fintype ι\ninst✝ : DecidableEq ι\n⊢ Function.RightInverse (invFun p) (toFun p)", "returncode": 1}

Corrected proof:

[Assistant]
by
  dsimp only [toFun, invFun]
  rw [Function.rightInverse_iff_comp, ← coe_comp, ← @id_coe R]
  congr
  refine pi_ext fun i x ↦ ?_
  induction x using Submodule.Quotient.induction_on with | _ x'
  refine funext fun j ↦ ?_
  rw [comp_apply, piQuotientLift_single, mapQ_apply,
    quotientPiLift_mk, id_apply]
  by_cases hij : i = j <;> simp only [mkQ_apply, coe_single]
  · subst hij
    rw [Pi.single_eq_same, Pi.single_eq_same]
  · rw [Pi.single_eq_of_ne (Ne.symm hij), Pi.single_eq_of_ne (Ne.symm hij), Quotient.mk_zero]

Prompt:
Repair the failed Lean proof using the exact public context below. Return only one corrected proof body beginning with `by`; no prose or fences.

Imports:
public import Mathlib.LinearAlgebra.Pi
public import Mathlib.LinearAlgebra.Quotient.Basic

Namespace:
Submodule.quotientPi_aux

Local safe context:
/-
Copyright (c) 2022 Anne Baanen. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Anne Baanen, Alex J. Best
-/
/-!
# Submodule quotients and direct sums

This file contains some results on the quotient of a module by a direct sum of submodules,
and the direct sum of quotients of modules by submodules.

## Main definitions

* `Submodule.piQuotientLift`: create a map out of the direct sum of quotients
* `Submodule.quotientPiLift`: create a map out of the quotient of a direct sum
* `Submodule.quotientPi`: the quotient of a direct sum is the direct sum of quotients.

-/

@[expose] public section

namespace Submodule

open LinearMap

variable {ι R : Type*} [CommRing R]
variable {Ms : ι → Type*} [∀ i, AddCommGroup (Ms i)] [∀ i, Module R (Ms i)]
variable {N : Type*} [AddCommGroup N] [Module R N]
variable {Ns : ι → Type*} [∀ i, AddCommGroup (Ns i)] [∀ i, Module R (Ns i)]

/-- Lift a family of maps to the direct sum of quotients. -/
def piQuotientLift [Fintype ι] [DecidableEq ι] (p : ∀ i, Submodule R (Ms i)) (q : Submodule R N)
    (f : ∀ i, Ms i →ₗ[R] N) (hf : ∀ i, p i ≤ q.comap (f i)) : (∀ i, Ms i ⧸ p i) →ₗ[R] N ⧸ q :=
  lsum R (fun i => Ms i ⧸ p i) R fun i => (p i).mapQ q (f i) (hf i)

@[simp]
theorem piQuotientLift_mk [Fintype ι] [DecidableEq ι] (p : ∀ i, Submodule R (Ms i))
    (q : Submodule R N) (f : ∀ i, Ms i →ₗ[R] N) (hf : ∀ i, p i ≤ q.comap (f i)) (x : ∀ i, Ms i) :
    (piQuotientLift p q f hf fun i => Quotient.mk (x i)) = Quotient.mk (lsum _ _ R f x) := by
  rw [piQuotientLift, lsum_apply, sum_apply, ← mkQ_apply, lsum_apply, sum_apply, _root_.map_sum]
  simp only [coe_proj, mapQ_apply, mkQ_apply, comp_apply]

@[simp]
theorem piQuotientLift_single [Fintype ι] [DecidableEq ι] (p : ∀ i, Submodule R (Ms i))
    (q : Submodule R N) (f : ∀ i, Ms i →ₗ[R] N) (hf : ∀ i, p i ≤ q.comap (f i)) (i)
    (x : Ms i ⧸ p i) : piQuotientLift p q f hf (Pi.single i x) = mapQ _ _ (f i) (hf i) x := by
  simp_rw [piQuotientLift, lsum_apply, sum_apply, comp_apply, proj_apply]
  rw [Finset.sum_eq_single i]
  · rw [Pi.single_eq_same]
  · rintro j - hj
    rw [Pi.single_eq_of_ne hj, map_zero]
  · intros
    have := Finset.mem_univ i
    contradiction

/-- Lift a family of maps to a quotient of direct sums. -/
def quotientPiLift (p : ∀ i, Submodule R (Ms i)) (f : ∀ i, Ms i →ₗ[R] Ns i)
    (hf : ∀ i, p i ≤ ker (f i)) : (∀ i, Ms i) ⧸ pi Set.univ p →ₗ[R] ∀ i, Ns i :=
  (pi Set.univ p).liftQ (LinearMap.pi fun i => (f i).comp (proj i)) fun x hx =>
    mem_ker.mpr <| by
      ext i
      simpa using hf i (mem_pi.mp hx i (Set.mem_univ i))

@[simp]
theorem quotientPiLift_mk (p : ∀ i, Submodule R (Ms i)) (f : ∀ i, Ms i →ₗ[R] Ns i)
    (hf : ∀ i, p i ≤ ker (f i)) (x : ∀ i, Ms i) :
    quotientPiLift p f hf (Quotient.mk x) = fun i => f i (x i) :=
  rfl

namespace quotientPi_aux

variable (p : ∀ i, Submodule R (Ms i))

@[simp]
def toFun : ((∀ i, Ms i) ⧸ pi Set.univ p) → ∀ i, Ms i ⧸ p i :=
  quotientPiLift p (fun i => (p i).mkQ) fun i => (ker_mkQ (p i)).ge

theorem map_add (x y : ((i : ι) → Ms i) ⧸ pi Set.univ p) :
    toFun p (x + y) = toFun p x + toFun p y :=
  LinearMap.map_add (quotientPiLift p (fun i => (p i).mkQ) fun i => (ker_mkQ (p i)).ge) x y

theorem map_smul (r : R) (x : ((i : ι) → Ms i) ⧸ pi Set.univ p) :
    toFun p (r • x) = (RingHom.id R r) • toFun p x :=
  LinearMap.map_smul (quotientPiLift p (fun i => (p i).mkQ) fun i => (ker_mkQ (p i)).ge) r x

variable [Fintype ι] [DecidableEq ι]

@[simp]
def invFun : (∀ i, Ms i ⧸ p i) → (∀ i, Ms i) ⧸ pi Set.univ p :=
  piQuotientLift p (pi Set.univ p) _ fun _ => le_comap_single_pi p

theorem left_inv : Function.LeftInverse (invFun p) (toFun p) := fun x =>
  Submodule.Quotient.induction_on _ x fun x' => by
    dsimp only [toFun, invFun]
    rw [quotientPiLift_mk p, funext fun i => (mkQ_apply (p i) (x' i)), piQuotientLift_mk p,
      lsum_single, id_apply]

Target:
theorem right_inv : Function.RightInverse (invFun p) (toFun p) :=

Failed candidate:
by
  rw [show ((fun x : Nat => x + 1703247) 0) = ((fun x : Nat => x + 1703247) 0) by rfl]
  dsimp only [toFun, invFun]
  rw [Function.rightInverse_iff_comp, ← coe_comp, ← @id_coe R]
  congr
  refine pi_ext fun i x ↦ ?_
  induction x using Submodule.Quotient.induction_on with | _ x'
  refine funext fun j ↦ ?_
  rw [comp_apply, piQuotientLift_single, mapQ_apply,
    quotientPiLift_mk, id_apply]
  by_cases hij : i = j <;> simp only [mkQ_apply, coe_single]
  · subst hij
    rw [Pi.single_eq_same, Pi.single_eq_same]
  · rw [Pi.single_eq_of_ne (Ne.symm hij), Pi.single_eq_of_ne (Ne.symm hij), Quotient.mk_zero]

Structured Lean error:
{"kind": "rewrite_no_match", "message": "<LEAN_FILE>:106:6: error: Tactic `rewrite` failed: Did not find an occurrence of the pattern\n  (fun x => x + 1703247) 0\nin the target expression\n  Function.RightInverse (invFun p) (toFun p)\n\nι : Type u_1\nR : Type u_2\ninst✝⁴ : CommRing R\nMs : ι → Type u_3\ninst✝³ : (i : ι) → AddCommGroup (Ms i)\ninst✝² : (i : ι) → Module R (Ms i)\np : (i : ι) → Submodule R (Ms i)\ninst✝¹ : Fintype ι\ninst✝ : DecidableEq ι\n⊢ Function.RightInverse (invFun p) (toFun p)", "returncode": 1}

Corrected proof:


<LEAN_FILE>:189:6: error: Tactic `rewrite` failed: Did not find an occurrence of the pattern
  (fun x => x + 13530007) 0
in the target expression
  ∃! χ, p.IsHomLift g χ ∧ χ ≫ φ = φ'

𝒮 : Type u₁
𝒳 : Type u₂
inst✝³ : Category.{v₁, u₁} 𝒮
inst✝² : Category.{v₂, u₂} 𝒳
p : 𝒳 ⥤ 𝒮
R S : 𝒮
a b : 𝒳
f : R ⟶ S
φ : a ⟶ b
inst✝¹ : p.IsStronglyCartesian f φ
R' : 𝒮
a' : 𝒳
g : R' ⟶ R
f' : R' ⟶ S
hf' : f' = g ≫ f
φ' : a' ⟶ b
inst✝ : p.IsHomLift f' φ'
⊢ ∃! χ, p.IsHomLift g χ ∧ χ ≫ φ = φ'

Response:
by
  subst_hom_lift p f' φ'; clear a b R S
  have : p.IsHomLift (g ≫ f) φ' := (hf' ▸ inferInstance)
  apply IsStronglyCartesian.universal_property' f

[User]
Repair the failed Lean proof using the exact public context below. Return only one corrected proof body beginning with `by`; no prose or fences.

Imports:
public import Mathlib.CategoryTheory.FiberedCategory.HomLift

Namespace:
CategoryTheory.Functor.IsStronglyCartesian

Local safe context:
/-
Copyright (c) 2024 Calle Sönne. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Paul Lezeau, Calle Sönne
-/
/-!
# Cartesian morphisms

This file defines Cartesian resp. strongly Cartesian morphisms with respect to a functor
`p : 𝒳 ⥤ 𝒮`.

This file has been adapted to `Mathlib/CategoryTheory/FiberedCategory/Cocartesian.lean`,
please try to change them in sync.

## Main definitions

`IsCartesian p f φ` expresses that `φ` is a Cartesian morphism lying over `f` with respect to `p` in
the sense of SGA 1 VI 5.1. This means that for any morphism `φ' : a' ⟶ b` lying over `f` there is
a unique morphism `τ : a' ⟶ a` lying over `𝟙 R`, such that `φ' = τ ≫ φ`.

`IsStronglyCartesian p f φ` expresses that `φ` is a strongly Cartesian morphism lying over `f` with
respect to `p`, see <https://stacks.math.columbia.edu/tag/02XK>.

## Implementation

The constructor of `IsStronglyCartesian` has been named `universal_property'`, and is mainly
intended to be used for constructing instances of this class. To use the universal property, we
generally recommended to use the lemma `IsStronglyCartesian.universal_property` instead. The
difference between the two is that the latter is more flexible with respect to non-definitional
equalities.

## References
* [A. Grothendieck, M. Raynaud, *SGA 1*](https://arxiv.org/abs/math/0206203)
* [Stacks: Fibred Categories](https://stacks.math.columbia.edu/tag/02XJ)
-/

@[expose] public section

universe v₁ v₂ u₁ u₂

open CategoryTheory Functor Category IsHomLift

namespace CategoryTheory.Functor

variable {𝒮 : Type u₁} {𝒳 : Type u₂} [Category.{v₁} 𝒮] [Category.{v₂} 𝒳] (p : 𝒳 ⥤ 𝒮)

section

variable {R S : 𝒮} {a b : 𝒳} (f : R ⟶ S) (φ : a ⟶ b)

/-- A morphism `φ : a ⟶ b` in `𝒳` lying over `f : R ⟶ S` in `𝒮` is Cartesian if for all
morphisms `φ' : a' ⟶ b`, also lying over `f`, there exists a unique morphism `χ : a' ⟶ a` lifting
`𝟙 R` such that `φ' = χ ≫ φ`.

See SGA 1 VI 5.1. -/
class IsCartesian : Prop where
  [toIsHomLift : IsHomLift p f φ]
  universal_property {a' : 𝒳} (φ' : a' ⟶ b) [IsHomLift p f φ'] :
      ∃! χ : a' ⟶ a, IsHomLift p (𝟙 R) χ ∧ χ ≫ φ = φ'
attribute [instance] IsCartesian.toIsHomLift

/-- A morphism `φ : a ⟶ b` in `𝒳` lying over `f : R ⟶ S` in `𝒮` is strongly Cartesian if for
all morphisms `φ' : a' ⟶ b` and all diagrams of the form
```
a'        a --φ--> b
|         |        |
v         v        v
R' --g--> R --f--> S
```
such that `φ'` lifts `g ≫ f`, there exists a lift `χ` of `g` such that `φ' = χ ≫ φ`. -/
@[stacks 02XK]
class IsStronglyCartesian : Prop where
  [toIsHomLift : IsHomLift p f φ]
  universal_property' {a' : 𝒳} (g : p.obj a' ⟶ R) (φ' : a' ⟶ b) [IsHomLift p (g ≫ f) φ'] :
      ∃! χ : a' ⟶ a, IsHomLift p g χ ∧ χ ≫ φ = φ'
attribute [instance] IsStronglyCartesian.toIsHomLift

end

namespace IsCartesian

variable {R S : 𝒮} {a b : 𝒳} (f : R ⟶ S) (φ : a ⟶ b) [IsCartesian p f φ]

section

variable {a' : 𝒳} (φ' : a' ⟶ b) [IsHomLift p f φ']

/-- Given a Cartesian morphism `φ : a ⟶ b` lying over `f : R ⟶ S` in `𝒳`, and another morphism
`φ' : a' ⟶ b` which also lifts `f`, then `IsCartesian.map f φ φ'` is the morphism `a' ⟶ a` lifting
`𝟙 R` obtained from the universal property of `φ`. -/
protected noncomputable def map : a' ⟶ a :=
  Classical.choose <| IsCartesian.universal_property (p := p) (f := f) (φ := φ) φ'

instance map_isHomLift : IsHomLift p (𝟙 R) (IsCartesian.map p f φ φ') :=
  (Classical.choose_spec <| IsCartesian.universal_property (p := p) (f := f) (φ := φ) φ').1.1

@[reassoc (attr := simp)]
lemma fac : IsCartesian.map p f φ φ' ≫ φ = φ' :=
  (Classical.choose_spec <| IsCartesian.universal_property (p := p) (f := f) (φ := φ) φ').1.2

/-- Given a Cartesian morphism `φ : a ⟶ b` lying over `f : R ⟶ S` in `𝒳`, and another morphism
`φ' : a' ⟶ b` which also lifts `f`. Then any morphism `ψ : a' ⟶ a` lifting `𝟙 R` such that
`g ≫ ψ = φ'` must equal the map induced from the universal property of `φ`. -/
lemma map_uniq (ψ : a' ⟶ a) [IsHomLift p (𝟙 R) ψ] (hψ : ψ ≫ φ = φ') :
    ψ = IsCartesian.map p f φ φ' :=
  (Classical.choose_spec <| IsCartesian.universal_property (p := p) (f := f) (φ := φ) φ').2
    ψ ⟨inferInstance, hψ⟩

end

/-- Given a Cartesian morphism `φ : a ⟶ b` lying over `f : R ⟶ S` in `𝒳`, and two morphisms
`ψ ψ' : a' ⟶ a` such that `ψ ≫ φ = ψ' ≫ φ`. Then we must have `ψ = ψ'`. -/
protected lemma ext (φ : a ⟶ b) [IsCartesian p f φ] {a' : 𝒳} (ψ ψ' : a' ⟶ a)
    [IsHomLift p (𝟙 R) ψ] [IsHomLift p (𝟙 R) ψ'] (h : ψ ≫ φ = ψ' ≫ φ) : ψ = ψ' := by
  rw [map_uniq p f φ (ψ ≫ φ) ψ rfl, map_uniq p f φ (ψ ≫ φ) ψ' h.symm]

@[simp]
lemma map_self : IsCartesian.map p f φ φ = 𝟙 a := by
  subst_hom_lift p f φ; symm
  apply map_uniq
  simp only [id_comp]

instance of_comp_iso {b' : 𝒳} (φ' : b ≅ b') [IsHomLift p (𝟙 S) φ'.hom] :
    IsCartesian p f (φ ≫ φ'.hom) where
  universal_property := by
    intro c ψ hψ
    use IsCartesian.map p f φ (ψ ≫ φ'.inv)
    refine ⟨⟨inferInstance, by simp only [fac_assoc, assoc, Iso.inv_hom_id, comp_id]⟩, ?_⟩
    rintro τ ⟨hτ₁, hτ₂⟩
    apply map_uniq
    rw [Iso.eq_comp_inv]
    simp only [assoc, hτ₂]

/-- The canonical isomorphism between the domains of two Cartesian arrows
lying over the same object. -/
@[simps]
noncomputable def domainUniqueUpToIso {a' : 𝒳} (φ' : a' ⟶ b) [IsCartesian p f φ'] : a' ≅ a where
  hom := IsCartesian.map p f φ φ'
  inv := IsCartesian.map p f φ' φ
  hom_inv_id := by
    subst_hom_lift p f φ'
    apply IsCartesian.ext p (p.map φ') φ'
    simp only [assoc, fac, id_comp]
  inv_hom_id := by
    subst_hom_lift p f φ
    apply IsCartesian.ext p (p.map φ) φ
    simp only [assoc, fac, id_comp]

instance domainUniqueUpToIso_inv_isHomLift {a' : 𝒳} (φ' : a' ⟶ b) [IsCartesian p f φ'] :
    IsHomLift p (𝟙 R) (domainUniqueUpToIso p f φ φ').hom :=
  domainUniqueUpToIso_hom p f φ φ' ▸ IsCartesian.map_isHomLift p f φ φ'

instance domainUniqueUpToIso_hom_isHomLift {a' : 𝒳} (φ' : a' ⟶ b) [IsCartesian p f φ'] :
    IsHomLift p (𝟙 R) (domainUniqueUpToIso p f φ φ').inv :=
  domainUniqueUpToIso_inv p f φ φ' ▸ IsCartesian.map_isHomLift p f φ' φ

/-- Precomposing a Cartesian morphism with an isomorphism lifting the identity is Cartesian. -/
instance of_iso_comp {a' : 𝒳} (φ' : a' ≅ a) [IsHomLift p (𝟙 R) φ'.hom] :
    IsCartesian p f (φ'.hom ≫ φ) where
  universal_property := by
    intro c ψ hψ
    use IsCartesian.map p f φ ψ ≫ φ'.inv
    refine ⟨⟨inferInstance, by simp⟩, ?_⟩
    rintro τ ⟨hτ₁, hτ₂⟩
    rw [Iso.eq_comp_inv]
    apply map_uniq
    simp only [assoc, hτ₂]

end IsCartesian

namespace IsStronglyCartesian

section

variable {R S : 𝒮} {a b : 𝒳} (f : R ⟶ S) (φ : a ⟶ b) [IsStronglyCartesian p f φ]

/-- The universal property of a strongly Cartesian morphism.

This lemma is more flexible with respect to non-definitional equalities than the field
`universal_property'` of `IsStronglyCartesian`. -/

Target:
lemma universal_property {R' : 𝒮} {a' : 𝒳} (g : R' ⟶ R) (f' : R' ⟶ S) (hf' : f' = g ≫ f)
    (φ' : a' ⟶ b) [IsHomLift p f' φ'] : ∃! χ : a' ⟶ a, IsHomLift p g χ ∧ χ ≫ φ = φ' :=

Failed candidate:
by
  rw [show ((fun x : Nat => x + 13530007) 0) = ((fun x : Nat => x + 13530007) 0) by rfl]
  subst_hom_lift p f' φ'; clear a b R S
  have : p.IsHomLift (g ≫ f) φ' := (hf' ▸ inferInstance)
  apply IsStronglyCartesian.universal_property' f

Structured Lean error:
{"kind": "rewrite_no_match", "message": "<LEAN_FILE>:189:6: error: Tactic `rewrite` failed: Did not find an occurrence of the pattern\n  (fun x => x + 13530007) 0\nin the target expression\n  ∃! χ, p.IsHomLift g χ ∧ χ ≫ φ = φ'\n\n𝒮 : Type u₁\n𝒳 : Type u₂\ninst✝³ : Category.{v₁, u₁} 𝒮\ninst✝² : Category.{v₂, u₂} 𝒳\np : 𝒳 ⥤ 𝒮\nR S : 𝒮\na b : 𝒳\nf : R ⟶ S\nφ : a ⟶ b\ninst✝¹ : p.IsStronglyCartesian f φ\nR' : 𝒮\na' : 𝒳\ng : R' ⟶ R\nf' : R' ⟶ S\nhf' : f' = g ≫ f\nφ' : a' ⟶ b\ninst✝ : p.IsHomLift f' φ'\n⊢ ∃! χ, p.IsHomLift g χ ∧ χ ≫ φ = φ'", "returncode": 1}

Corrected proof:

[Assistant]
by
  subst_hom_lift p f' φ'; clear a b R S
  have : p.IsHomLift (g ≫ f) φ' := (hf' ▸ inferInstance)
  apply IsStronglyCartesian.universal_property' f

Prompt:
Repair the failed Lean proof using the exact public context below. Return only one corrected proof body beginning with `by`; no prose or fences.

Imports:
public import Mathlib.CategoryTheory.FiberedCategory.HomLift

Namespace:
CategoryTheory.Functor.IsStronglyCartesian

Local safe context:
/-
Copyright (c) 2024 Calle Sönne. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Paul Lezeau, Calle Sönne
-/
/-!
# Cartesian morphisms

This file defines Cartesian resp. strongly Cartesian morphisms with respect to a functor
`p : 𝒳 ⥤ 𝒮`.

This file has been adapted to `Mathlib/CategoryTheory/FiberedCategory/Cocartesian.lean`,
please try to change them in sync.

## Main definitions

`IsCartesian p f φ` expresses that `φ` is a Cartesian morphism lying over `f` with respect to `p` in
the sense of SGA 1 VI 5.1. This means that for any morphism `φ' : a' ⟶ b` lying over `f` there is
a unique morphism `τ : a' ⟶ a` lying over `𝟙 R`, such that `φ' = τ ≫ φ`.

`IsStronglyCartesian p f φ` expresses that `φ` is a strongly Cartesian morphism lying over `f` with
respect to `p`, see <https://stacks.math.columbia.edu/tag/02XK>.

## Implementation

The constructor of `IsStronglyCartesian` has been named `universal_property'`, and is mainly
intended to be used for constructing instances of this class. To use the universal property, we
generally recommended to use the lemma `IsStronglyCartesian.universal_property` instead. The
difference between the two is that the latter is more flexible with respect to non-definitional
equalities.

## References
* [A. Grothendieck, M. Raynaud, *SGA 1*](https://arxiv.org/abs/math/0206203)
* [Stacks: Fibred Categories](https://stacks.math.columbia.edu/tag/02XJ)
-/

@[expose] public section

universe v₁ v₂ u₁ u₂

open CategoryTheory Functor Category IsHomLift

namespace CategoryTheory.Functor

variable {𝒮 : Type u₁} {𝒳 : Type u₂} [Category.{v₁} 𝒮] [Category.{v₂} 𝒳] (p : 𝒳 ⥤ 𝒮)

section

variable {R S : 𝒮} {a b : 𝒳} (f : R ⟶ S) (φ : a ⟶ b)

/-- A morphism `φ : a ⟶ b` in `𝒳` lying over `f : R ⟶ S` in `𝒮` is Cartesian if for all
morphisms `φ' : a' ⟶ b`, also lying over `f`, there exists a unique morphism `χ : a' ⟶ a` lifting
`𝟙 R` such that `φ' = χ ≫ φ`.

See SGA 1 VI 5.1. -/
class IsCartesian : Prop where
  [toIsHomLift : IsHomLift p f φ]
  universal_property {a' : 𝒳} (φ' : a' ⟶ b) [IsHomLift p f φ'] :
      ∃! χ : a' ⟶ a, IsHomLift p (𝟙 R) χ ∧ χ ≫ φ = φ'
attribute [instance] IsCartesian.toIsHomLift

/-- A morphism `φ : a ⟶ b` in `𝒳` lying over `f : R ⟶ S` in `𝒮` is strongly Cartesian if for
all morphisms `φ' : a' ⟶ b` and all diagrams of the form
```
a'        a --φ--> b
|         |        |
v         v        v
R' --g--> R --f--> S
```
such that `φ'` lifts `g ≫ f`, there exists a lift `χ` of `g` such that `φ' = χ ≫ φ`. -/
@[stacks 02XK]
class IsStronglyCartesian : Prop where
  [toIsHomLift : IsHomLift p f φ]
  universal_property' {a' : 𝒳} (g : p.obj a' ⟶ R) (φ' : a' ⟶ b) [IsHomLift p (g ≫ f) φ'] :
      ∃! χ : a' ⟶ a, IsHomLift p g χ ∧ χ ≫ φ = φ'
attribute [instance] IsStronglyCartesian.toIsHomLift

end

namespace IsCartesian

variable {R S : 𝒮} {a b : 𝒳} (f : R ⟶ S) (φ : a ⟶ b) [IsCartesian p f φ]

section

variable {a' : 𝒳} (φ' : a' ⟶ b) [IsHomLift p f φ']

/-- Given a Cartesian morphism `φ : a ⟶ b` lying over `f : R ⟶ S` in `𝒳`, and another morphism
`φ' : a' ⟶ b` which also lifts `f`, then `IsCartesian.map f φ φ'` is the morphism `a' ⟶ a` lifting
`𝟙 R` obtained from the universal property of `φ`. -/
protected noncomputable def map : a' ⟶ a :=
  Classical.choose <| IsCartesian.universal_property (p := p) (f := f) (φ := φ) φ'

instance map_isHomLift : IsHomLift p (𝟙 R) (IsCartesian.map p f φ φ') :=
  (Classical.choose_spec <| IsCartesian.universal_property (p := p) (f := f) (φ := φ) φ').1.1

@[reassoc (attr := simp)]
lemma fac : IsCartesian.map p f φ φ' ≫ φ = φ' :=
  (Classical.choose_spec <| IsCartesian.universal_property (p := p) (f := f) (φ := φ) φ').1.2

/-- Given a Cartesian morphism `φ : a ⟶ b` lying over `f : R ⟶ S` in `𝒳`, and another morphism
`φ' : a' ⟶ b` which also lifts `f`. Then any morphism `ψ : a' ⟶ a` lifting `𝟙 R` such that
`g ≫ ψ = φ'` must equal the map induced from the universal property of `φ`. -/
lemma map_uniq (ψ : a' ⟶ a) [IsHomLift p (𝟙 R) ψ] (hψ : ψ ≫ φ = φ') :
    ψ = IsCartesian.map p f φ φ' :=
  (Classical.choose_spec <| IsCartesian.universal_property (p := p) (f := f) (φ := φ) φ').2
    ψ ⟨inferInstance, hψ⟩

end

/-- Given a Cartesian morphism `φ : a ⟶ b` lying over `f : R ⟶ S` in `𝒳`, and two morphisms
`ψ ψ' : a' ⟶ a` such that `ψ ≫ φ = ψ' ≫ φ`. Then we must have `ψ = ψ'`. -/
protected lemma ext (φ : a ⟶ b) [IsCartesian p f φ] {a' : 𝒳} (ψ ψ' : a' ⟶ a)
    [IsHomLift p (𝟙 R) ψ] [IsHomLift p (𝟙 R) ψ'] (h : ψ ≫ φ = ψ' ≫ φ) : ψ = ψ' := by
  rw [map_uniq p f φ (ψ ≫ φ) ψ rfl, map_uniq p f φ (ψ ≫ φ) ψ' h.symm]

@[simp]
lemma map_self : IsCartesian.map p f φ φ = 𝟙 a := by
  subst_hom_lift p f φ; symm
  apply map_uniq
  simp only [id_comp]

instance of_comp_iso {b' : 𝒳} (φ' : b ≅ b') [IsHomLift p (𝟙 S) φ'.hom] :
    IsCartesian p f (φ ≫ φ'.hom) where
  universal_property := by
    intro c ψ hψ
    use IsCartesian.map p f φ (ψ ≫ φ'.inv)
    refine ⟨⟨inferInstance, by simp only [fac_assoc, assoc, Iso.inv_hom_id, comp_id]⟩, ?_⟩
    rintro τ ⟨hτ₁, hτ₂⟩
    apply map_uniq
    rw [Iso.eq_comp_inv]
    simp only [assoc, hτ₂]

/-- The canonical isomorphism between the domains of two Cartesian arrows
lying over the same object. -/
@[simps]
noncomputable def domainUniqueUpToIso {a' : 𝒳} (φ' : a' ⟶ b) [IsCartesian p f φ'] : a' ≅ a where
  hom := IsCartesian.map p f φ φ'
  inv := IsCartesian.map p f φ' φ
  hom_inv_id := by
    subst_hom_lift p f φ'
    apply IsCartesian.ext p (p.map φ') φ'
    simp only [assoc, fac, id_comp]
  inv_hom_id := by
    subst_hom_lift p f φ
    apply IsCartesian.ext p (p.map φ) φ
    simp only [assoc, fac, id_comp]

instance domainUniqueUpToIso_inv_isHomLift {a' : 𝒳} (φ' : a' ⟶ b) [IsCartesian p f φ'] :
    IsHomLift p (𝟙 R) (domainUniqueUpToIso p f φ φ').hom :=
  domainUniqueUpToIso_hom p f φ φ' ▸ IsCartesian.map_isHomLift p f φ φ'

instance domainUniqueUpToIso_hom_isHomLift {a' : 𝒳} (φ' : a' ⟶ b) [IsCartesian p f φ'] :
    IsHomLift p (𝟙 R) (domainUniqueUpToIso p f φ φ').inv :=
  domainUniqueUpToIso_inv p f φ φ' ▸ IsCartesian.map_isHomLift p f φ' φ

/-- Precomposing a Cartesian morphism with an isomorphism lifting the identity is Cartesian. -/
instance of_iso_comp {a' : 𝒳} (φ' : a' ≅ a) [IsHomLift p (𝟙 R) φ'.hom] :
    IsCartesian p f (φ'.hom ≫ φ) where
  universal_property := by
    intro c ψ hψ
    use IsCartesian.map p f φ ψ ≫ φ'.inv
    refine ⟨⟨inferInstance, by simp⟩, ?_⟩
    rintro τ ⟨hτ₁, hτ₂⟩
    rw [Iso.eq_comp_inv]
    apply map_uniq
    simp only [assoc, hτ₂]

end IsCartesian

namespace IsStronglyCartesian

section

variable {R S : 𝒮} {a b : 𝒳} (f : R ⟶ S) (φ : a ⟶ b) [IsStronglyCartesian p f φ]

/-- The universal property of a strongly Cartesian morphism.

This lemma is more flexible with respect to non-definitional equalities than the field
`universal_property'` of `IsStronglyCartesian`. -/

Target:
lemma universal_property {R' : 𝒮} {a' : 𝒳} (g : R' ⟶ R) (f' : R' ⟶ S) (hf' : f' = g ≫ f)
    (φ' : a' ⟶ b) [IsHomLift p f' φ'] : ∃! χ : a' ⟶ a, IsHomLift p g χ ∧ χ ≫ φ = φ' :=

Failed candidate:
by
  rw [show ((fun x : Nat => x + 13530007) 0) = ((fun x : Nat => x + 13530007) 0) by rfl]
  subst_hom_lift p f' φ'; clear a b R S
  have : p.IsHomLift (g ≫ f) φ' := (hf' ▸ inferInstance)
  apply IsStronglyCartesian.universal_property' f

Structured Lean error:
{"kind": "rewrite_no_match", "message": "<LEAN_FILE>:189:6: error: Tactic `rewrite` failed: Did not find an occurrence of the pattern\n  (fun x => x + 13530007) 0\nin the target expression\n  ∃! χ, p.IsHomLift g χ ∧ χ ≫ φ = φ'\n\n𝒮 : Type u₁\n𝒳 : Type u₂\ninst✝³ : Category.{v₁, u₁} 𝒮\ninst✝² : Category.{v₂, u₂} 𝒳\np : 𝒳 ⥤ 𝒮\nR S : 𝒮\na b : 𝒳\nf : R ⟶ S\nφ : a ⟶ b\ninst✝¹ : p.IsStronglyCartesian f φ\nR' : 𝒮\na' : 𝒳\ng : R' ⟶ R\nf' : R' ⟶ S\nhf' : f' = g ≫ f\nφ' : a' ⟶ b\ninst✝ : p.IsHomLift f' φ'\n⊢ ∃! χ, p.IsHomLift g χ ∧ χ ≫ φ = φ'", "returncode": 1}

Corrected proof: