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import OAI.Combinatorics.GraphThreshold.ProbabilityTreeTrim
import OAI.Combinatorics.GraphThreshold.CapacityIteration
import OAI.Combinatorics.GraphThreshold.AdaptiveTrials
import OAI.Combinatorics.GraphThreshold.TreeReduction
import OAI.Combinatorics.GraphThreshold.BernoulliMonotonicity
import OAI.Combinatorics.GraphThreshold.TreePotential
import Mathlib.Tactic
namespace OAI
/-!
# Covering a probability tree by iterative reductions
Recovery keeps the original and retained path histories distinct, even when
their labels agree. All draws are retained in the accumulating union.
-/
noncomputable section
open Classical
namespace LeanBlast.SecondKahnKalai
/-- A nondecreasing finite list of capacities has a zero prefix followed by
strictly positive capacities. The empty positive suffix is permitted. -/
theorem exists_zero_prefix_positive_suffix (m : ℕ → ℕ) (d : ℕ)
(hmono : MonotoneOn m (Set.Iio d)) :
∃ k, k ≤ d ∧ (∀ i, i < k → m i = 0) ∧
(∀ i, i < d - k → 0 < m (i + k)) := by
classical
by_cases h : ∃ k, k < d ∧ 0 < m k
· let k := Nat.find h
have hk : k < d ∧ 0 < m k := Nat.find_spec h
refine ⟨k, hk.1.le, ?_, ?_⟩
· intro i hi
by_contra hzero
have hip : 0 < m i := Nat.pos_of_ne_zero hzero
have hki : k ≤ i := Nat.find_min' h ⟨lt_trans hi hk.1, hip⟩
omega
· intro i hi
have hik : i + k < d := by omega
exact lt_of_lt_of_le hk.2 (hmono hk.1 hik (by omega))
· refine ⟨d, le_rfl, ?_, ?_⟩
· intro i hi
by_contra hzero
exact h ⟨i, hi, Nat.pos_of_ne_zero hzero⟩
· intro i hi
omega
theorem capacityReserve_div_sampling_le {σ : ℝ} (hσ : 0 < σ) (m : ℕ) :
capacityReserve σ m / (Real.exp 50 * (4 * σ)) ≤ Real.exp (-50) := by
have hp : 0 < Real.exp 50 * (4 * σ) := by positivity
calc
_ ≤ (4 * σ) / (Real.exp 50 * (4 * σ)) :=
div_le_div_of_nonneg_right (capacityReserve_upper hσ.le m) hp.le
_ = Real.exp (-50) := by
rw [Real.exp_neg]
field_simp
theorem sampling_budget_le {σ : ℝ} (hσ : 0 ≤ σ) (L : ℕ) :
((4 * successesNeeded L : ℕ) : ℝ) * (Real.exp 50 * (4 * σ)) ≤
16 * Real.exp 50 * σ * (1 + Real.logb 2 (L : ℝ)) := by
calc
_ = (16 * Real.exp 50 * σ) * (successesNeeded L : ℝ) := by push_cast; ring
_ ≤ _ := mul_le_mul_of_nonneg_left (successesNeeded_le_logb L) (by positivity)
namespace ProbabilityTree
variable {X : Type} [DecidableEq X]
/-- Each path of a retained tree recovers a path of the original tree after
the already collected coordinates are added. -/
def Recovers {d e : ℕ} (T : ProbabilityTree X d) (S : ProbabilityTree X e)
(W : Finset X) : Prop :=
∀ q : S.Path, ∃ p : T.Path, T.pathUnion p ⊆ W ∪ S.pathUnion q
theorem Recovers.refl {d : ℕ} (T : ProbabilityTree X d) : Recovers T T ∅ := by
intro p
exact ⟨p, by simp⟩
theorem Recovers.mono {d e : ℕ} {T : ProbabilityTree X d} {S : ProbabilityTree X e}
{W V : Finset X} (h : Recovers T S W) (hWV : W ⊆ V) : Recovers T S V := by
intro q
obtain ⟨p, hp⟩ := h q
exact ⟨p, hp.trans (Finset.union_subset_union hWV (Finset.Subset.refl _))⟩
/-- Recovery composes through the union of the independent draws. -/
theorem Recovers.trans {d e f : ℕ}
{T : ProbabilityTree X d} {S : ProbabilityTree X e} {U : ProbabilityTree X f}
{W V : Finset X} (hTS : Recovers T S W) (hSU : Recovers S U V) :
Recovers T U (W ∪ V) := by
intro r
obtain ⟨q, hq⟩ := hSU r
obtain ⟨p, hp⟩ := hTS q
refine ⟨p, ?_⟩
simpa only [Finset.union_assoc] using
hp.trans (Finset.union_subset_union (Finset.Subset.refl W) hq)
/-- A covered retained path yields a covered original path. -/
theorem Recovers.coveredBy {d e : ℕ} {T : ProbabilityTree X d} {S : ProbabilityTree X e}
{W V : Finset X} (h : Recovers T S W) (hS : S.CoveredBy V) :
T.CoveredBy (W ∪ V) := by
obtain ⟨q, hq⟩ := hS
obtain ⟨p, hp⟩ := h q
exact ⟨p, hp.trans (Finset.union_subset_union (Finset.Subset.refl W) hq)⟩
/-- When no levels remain, recovery is already a covering certificate. -/
theorem Recovers.coveredBy_of_depth_zero {d : ℕ} {T : ProbabilityTree X d}
{S : ProbabilityTree X 0} {W : Finset X} (h : Recovers T S W) : T.CoveredBy W := by
cases S
obtain ⟨p, hp⟩ := h PUnit.unit
exact ⟨p, by simpa only [pathUnion, Finset.union_empty] using hp⟩
theorem Recovers.coveredBy_of_depth_eq_zero {d e : ℕ} {T : ProbabilityTree X d}
{S : ProbabilityTree X e} {W : Finset X} (h : Recovers T S W) (he : e = 0) :
T.CoveredBy W := by
subst e
exact h.coveredBy_of_depth_zero
/-- Removing empty initial labels preserves recovery without adding any
coordinates. The path lifting premise is supplied by deterministic prefix
removal. -/
theorem Recovers.of_pathUnion_eq {d e : ℕ}
{T : ProbabilityTree X d} {S : ProbabilityTree X e}
(h : ∀ q : S.Path, ∃ p : T.Path, T.pathUnion p = S.pathUnion q) :
Recovers T S ∅ := by
intro q
obtain ⟨p, hp⟩ := h q
exact ⟨p, by simp [hp]⟩
/-- Increasing each nonnegative level spread parameter preserves spread. -/
theorem HasSpread.mono {d : ℕ} {T : ProbabilityTree X d} {a b : ℕ → ℝ}
(hT : T.HasSpread a) (ha : ∀ i, i < d → 0 ≤ a i)
(hab : ∀ i, i < d → a i ≤ b i) : T.HasSpread b := by
induction T generalizing a b with
| leaf => trivial
| @node d B inst law positive label child ih =>
constructor
· intro J hJ
exact (hT.1 J hJ).trans (pow_le_pow_left₀ (ha 0 (by omega)) (hab 0 (by omega)) _)
· intro c
exact ih c (hT.2 c) (fun i hi => ha (i + 1) (by omega))
(fun i hi => hab (i + 1) (by omega))
theorem coveredBy_probability_one [Fintype X] {d : ℕ} (T : ProbabilityTree X d) :
bernoulliProbability 1 T.CoveredBy = 1 := by
apply le_antisymm
· exact (bernoulliLaw 1 (by norm_num) le_rfl).prob_le_one T.CoveredBy
· have h := (bernoulliLaw (X := X) 1 (by norm_num) le_rfl).prob_mono
(P := fun W => Finset.univ ⊆ W) (Q := T.CoveredBy)
(fun _ hW => coveredBy_mono (coveredBy_univ T) hW)
change bernoulliProbability 1 (fun W => Finset.univ ⊆ W) ≤
bernoulliProbability 1 T.CoveredBy at h
simpa only [bernoulliProbability_subset, one_pow] using h
/-- The actual retained tree, its spread budget, and recovery to the fixed
original tree. Only positive-capacity levels are stored. -/
structure CoverState {k : ℕ} (original : ProbabilityTree X k) (σ : ℝ) where
depth : ℕ
tree : ProbabilityTree X depth
capacity : ℕ → ℕ
disjoint : tree.IsDisjoint
capacities : tree.HasCapacities capacity
spread : tree.HasSpread (fun i => capacityReserve σ (capacity i))
positive : ∀ i, i < depth → 0 < capacity i
growth : ∀ i, i + 1 < depth → 16 * capacity i ≤ capacity (i + 1)
seen : Finset X
recovery : Recovers original tree seen
namespace CoverState
variable {k : ℕ} {original : ProbabilityTree X k} {σ : ℝ}
def initial (original : ProbabilityTree X k) (σ : ℝ) (m : ℕ → ℕ)
(hσ : 0 < σ) (hdisjoint : original.IsDisjoint)
(hcapacity : original.HasCapacities m)
(hspread : original.HasSpread (fun _ => σ))
(hpositive : ∀ i, i < k → 0 < m i)
(hgrowth : ∀ i, i + 1 < k → 16 * m i ≤ m (i + 1)) : CoverState original σ :=
{ depth := k
tree := original
capacity := m
disjoint := hdisjoint
capacities := hcapacity
spread := hspread.mono (fun _ _ => hσ.le) (fun i _ => capacityReserve_lower hσ.le (m i))
positive := hpositive
growth := hgrowth
seen := ∅
recovery := Recovers.refl original }
def rank (state : CoverState original σ) : ℕ :=
if state.depth = 0 then 0 else successesNeeded (state.capacity (state.depth - 1))
@[simp] theorem rank_eq_zero_iff (state : CoverState original σ) :
state.rank = 0 ↔ state.depth = 0 := by
unfold rank
split_ifs with h
· simp [h]
· simp [h, ne_of_gt (successesNeeded_pos _)]
theorem coveredBy_of_rank_zero (state : CoverState original σ) (h : state.rank = 0) :
original.CoveredBy state.seen :=
state.recovery.coveredBy_of_depth_eq_zero ((rank_eq_zero_iff state).mp h)
/-- Every draw is retained even when the reduction attempt fails. -/
def accumulate (state : CoverState original σ) (W : Finset X) : CoverState original σ :=
{ state with
seen := state.seen ∪ W
recovery := state.recovery.mono Finset.subset_union_left }
@[simp] theorem accumulate_rank (state : CoverState original σ) (W : Finset X) :
(state.accumulate W).rank = state.rank := rfl
def Advances (state : CoverState original σ) (W : Finset X)
(next : CoverState original σ) : Prop :=
next.rank < state.rank ∧ next.seen = state.seen ∪ W
/-- Choose a strict improvement when one exists; otherwise keep the tree.
Existence of improvements will be supplied by the actual good-tree reduction. -/
def step (state : CoverState original σ) (W : Finset X) : CoverState original σ :=
if h : ∃ next, state.Advances W next then Classical.choose h else state.accumulate W
theorem step_seen (state : CoverState original σ) (W : Finset X) :
(state.step W).seen = state.seen ∪ W := by
unfold step
split_ifs with h
· exact (Classical.choose_spec h).2
· rfl
theorem step_rank_le (state : CoverState original σ) (W : Finset X) :
(state.step W).rank ≤ state.rank := by
unfold step
split_ifs with h
· exact (Classical.choose_spec h).1.le
· exact le_rfl
theorem step_rank_lt_of_exists (state : CoverState original σ) (W : Finset X)
(h : ∃ next, state.Advances W next) : (state.step W).rank < state.rank := by
unfold step
rw [dite_eq_left h]
exact (Classical.choose_spec h).1
theorem biUnion_fin_succ {n : ℕ} (draws : Fin (n + 1) → Finset X) :
Finset.univ.biUnion draws = draws 0 ∪ Finset.univ.biUnion (fun i : Fin n => draws i.succ) := by
ext x
simp only [Finset.mem_biUnion, Finset.mem_univ, true_and, Finset.mem_union]
constructor
· rintro ⟨i, hi⟩
refine Fin.cases (fun hx => Or.inl hx) (fun j hx => Or.inr ⟨j, hx⟩) i hi
· rintro (h | ⟨i, hi⟩)
· exact ⟨0, h⟩
· exact ⟨i.succ, hi⟩
/-- The recorded set is exactly the union of all draws, including failures. -/
theorem run_seen (n : ℕ) (state : CoverState original σ) (draws : Fin n → Finset X) :
(adaptiveRun step n state draws).seen = state.seen ∪ Finset.univ.biUnion draws := by
induction n generalizing state with
| zero => simp [adaptiveRun]
| succ n ih =>
rw [adaptiveRun, ih, step_seen, biUnion_fin_succ, Finset.union_assoc]
/-- The finite adaptive theorem transfers actual strict advances to covering.
The good-tree probability estimate supplies the premise in the final theorem. -/
theorem prob_covered_of_advance_probability [Fintype X] (μ : FiniteLaw (Finset X))
(hprogress : ∀ state : CoverState original σ, state.rank ≠ 0 →
(3 / 4 : ℝ) ≤ μ.prob (fun W => ∃ next, state.Advances W next))
(s : ℕ) (state : CoverState original σ) (hrank : state.rank ≤ s) :
(2 / 3 : ℝ) ≤ (μ.iid (4 * s)).prob
(fun draws => original.CoveredBy (state.seen ∪ Finset.univ.biUnion draws)) := by
have hp : ∀ st : CoverState original σ, st.rank ≠ 0 →
(3 / 4 : ℝ) ≤ μ.prob (fun W => (st.step W).rank < st.rank) := by
intro st hst
exact (hprogress st hst).trans (μ.prob_mono fun W hW => st.step_rank_lt_of_exists W hW)
have hcomplete := adaptive_rank_completion μ rank step step_rank_le hp s state hrank
apply hcomplete.trans
apply (μ.iid (4 * s)).prob_mono
intro draws hdraws
have hcover := (adaptiveRun step (4 * s) state draws).coveredBy_of_rank_zero hdraws
rwa [run_seen] at hcover
/-- A halved tree, after its zero prefix is removed, is a strict improvement
of the current positive-capacity tree. -/
theorem exists_advance_of_halved (state : CoverState original σ) (W : Finset X)
(hdepth : state.depth ≠ 0) (U : ProbabilityTree X state.depth)
(hdisjoint : U.IsDisjoint)
(hcapacity : U.HasCapacities (fun i => state.capacity i / 2))
(hspread : U.HasSpread (fun i => capacityReserve σ (state.capacity i / 2)))
(hrecovery : Recovers state.tree U W) :
∃ next, state.Advances W next := by
let m : ℕ → ℕ := fun i => state.capacity i / 2
have hgrowth : ∀ i, i + 1 < state.depth → 16 * m i ≤ m (i + 1) := by
intro i hi
simpa [m, reducedCapacity] using reducedCapacity_growth (state.growth i hi) 1
obtain ⟨j, hj, hzero, hpositive⟩ := exists_zero_prefix_positive_suffix m state.depth
(monotoneOn_capacities m state.depth hgrowth)
let V := U.dropPrefix j hj
have htrim : Recovers U V ∅ := by
apply Recovers.of_pathUnion_eq
intro q
exact ⟨liftDropPrefixPath U j hj q,
pathUnion_liftDropPrefixPath_eq hcapacity j hj hzero q⟩
let next : CoverState original σ :=
{ depth := state.depth - j
tree := V
capacity := fun i => m (i + j)
disjoint := dropPrefix_isDisjoint hdisjoint j hj
capacities := dropPrefix_hasCapacities hcapacity j hj
spread := dropPrefix_hasSpread hspread j hj
positive := hpositive
growth := by
intro i hi
simpa only [Nat.add_assoc, Nat.add_comm 1 j] using hgrowth (i + j) (by omega)
seen := state.seen ∪ W
recovery := by
simpa only [Finset.union_empty] using (state.recovery.trans hrecovery).trans htrim }
refine ⟨next, ?_, rfl⟩
change (if state.depth - j = 0 then 0 else
successesNeeded (m (state.depth - j - 1 + j))) < state.rank
by_cases hempty : state.depth - j = 0
· rw [ite_eq_left hempty]
exact Nat.pos_of_ne_zero (fun h => hdepth ((rank_eq_zero_iff state).mp h))
· rw [ite_eq_right hempty]
have hindex : state.depth - j - 1 + j = state.depth - 1 := by omega
rw [hindex]
unfold rank
rw [ite_eq_right hdepth]
apply successesNeeded_half_lt
have hp := hpositive (state.depth - j - 1) (by omega)
simpa only [hindex] using hp
/-- A good draw produces an actual strict advance: construct the pruned tree,
preserve the reserve budget, and delete exactly its zero-capacity prefix. -/
theorem exists_advance_of_good (state : CoverState original σ) (W : Finset X)
(hσ : 0 < σ) {ρ : ℝ} (hρ : 0 < ρ) (hrank : state.rank ≠ 0)
(hgood : Good ρ state.capacity W state.tree) :
∃ next, state.Advances W next := by
let U := reduceTree ρ state.capacity W state.tree hρ state.positive hgood
have ha : ∀ i, i < state.depth → 0 ≤ capacityReserve σ (state.capacity i) :=
fun i _ => (capacityReserve_pos hσ (state.capacity i)).le
have hspread := reduceTree_hasSpread ρ state.capacity W state.tree hρ state.positive
hgood (fun i => capacityReserve σ (state.capacity i)) ha state.spread
refine state.exists_advance_of_halved W
(fun hd => hrank ((rank_eq_zero_iff state).mpr hd)) U
(reduceTree_isDisjoint ρ state.capacity W state.tree hρ state.positive hgood state.disjoint)
(reduceTree_hasCapacities ρ state.capacity W state.tree hρ state.positive hgood) ?_
(reduceTree_path_recovery ρ state.capacity W state.tree hρ state.positive hgood)
exact hspread.mono
(fun i hi => div_nonneg (ha i hi) (retentionFactor_pos (state.positive i hi)).le)
(fun i hi => capacityReserve_div_le_half hσ.le (state.positive i hi))
end CoverState
end ProbabilityTree
/-- The finite random experiment and final parameter comparison. The next
theorem supplies this private lemma's progress estimate from actual reduction. -/
private theorem tree_covering_of_progress {X : Type} [Fintype X] [DecidableEq X]
{k : ℕ} (T : ProbabilityTree X k) (hk : 0 < k) (hdis : T.IsDisjoint)
(m : ℕ → ℕ) (hcap : T.HasCapacities m) (hpos : ∀ i, i < k → 0 < m i)
(hgrowth : ∀ i, i + 1 < k → 16 * m i ≤ m (i + 1))
(σ : ℝ) (hσ : 0 < σ) (hspread : T.HasSpread (fun _ => σ))
(hprogress : Real.exp 50 * (4 * σ) < 1 →
∀ state : ProbabilityTree.CoverState T σ, state.rank ≠ 0 →
(3 / 4 : ℝ) ≤ bernoulliProbability (Real.exp 50 * (4 * σ))
(fun W => ∃ next, state.Advances W next)) :
(2 / 3 : ℝ) ≤ bernoulliProbability
(min 1 (16 * Real.exp 50 * σ * (1 + Real.logb 2 (m (k - 1) : ℝ)))) T.CoveredBy := by
let B := 16 * Real.exp 50 * σ * (1 + Real.logb 2 (m (k - 1) : ℝ))
change (2 / 3 : ℝ) ≤ bernoulliProbability (min 1 B) T.CoveredBy
by_cases hB : 1 ≤ B
· rw [min_eq_left hB, ProbabilityTree.coveredBy_probability_one]
norm_num
have hB1 : B < 1 := lt_of_not_ge hB
let p := Real.exp 50 * (4 * σ)
have hp : 0 < p := by dsimp [p]; positivity
have hlog : 0 ≤ Real.logb 2 (m (k - 1) : ℝ) :=
capacity_logb_nonneg (hpos (k - 1) (by omega))
have hBp : 4 * p ≤ B := by
calc
4 * p = (16 * Real.exp 50 * σ) * 1 := by dsimp [p]; ring
_ ≤ B := mul_le_mul_of_nonneg_left (by linarith : (1 : ℝ) ≤
1 + Real.logb 2 (m (k - 1) : ℝ)) (by positivity)
have hp1 : p < 1 := by linarith
let μ := bernoulliLaw (X := X) p hp.le hp1.le
let state := ProbabilityTree.CoverState.initial T σ m hσ hdis hcap hspread hpos hgrowth
let s := successesNeeded (m (k - 1))
have hrank : state.rank ≤ s := by
change (if k = 0 then 0 else successesNeeded (m (k - 1))) ≤ s
rw [ite_eq_right (Nat.ne_of_gt hk)]
have hprog : ∀ st : ProbabilityTree.CoverState T σ, st.rank ≠ 0 →
(3 / 4 : ℝ) ≤ μ.prob (fun W => ∃ next, st.Advances W next) :=
fun st hst => hprogress hp1 st hst
have hc := ProbabilityTree.CoverState.prob_covered_of_advance_probability μ hprog s state hrank
have hseen : state.seen = ∅ := rfl
simp only [hseen, Finset.empty_union] at hc
change (2 / 3 : ℝ) ≤ ((bernoulliLaw p hp.le hp1.le).iid (4 * s)).prob
(fun draws => T.CoveredBy (Finset.univ.biUnion draws)) at hc
rw [iid_bernoulli_union_probability] at hc
have hq0 := (bernoulli_union_parameter_mem hp.le hp1.le (4 * s)).1
have hqB : 1 - (1 - p) ^ (4 * s) ≤ B :=
(bernoulli_union_parameter_le hp.le hp1.le (4 * s)).trans
(sampling_budget_le hσ.le (m (k - 1)))
have hmono := bernoulliProbability_mono_parameter hq0 hqB hB1.le T.CoveredBy
(fun _ _ hUV hU => ProbabilityTree.coveredBy_mono hU hUV)
rw [min_eq_right hB1.le]
exact hc.trans hmono
theorem tree_covering {X : Type} [Fintype X] [DecidableEq X] {k : ℕ}
(T : ProbabilityTree X k) (hk : 0 < k) (hdis : T.IsDisjoint)
(m : ℕ → ℕ) (hcap : T.HasCapacities m) (hpos : ∀ i, i < k → 0 < m i)
(hgrowth : ∀ i, i + 1 < k → 16 * m i ≤ m (i + 1))
(σ : ℝ) (hσ : 0 < σ) (hspread : T.HasSpread (fun _ => σ)) :
(2 / 3 : ℝ) ≤ bernoulliProbability
(min 1 (16 * Real.exp 50 * σ * (1 + Real.logb 2 (m (k - 1) : ℝ)))) T.CoveredBy := by
apply tree_covering_of_progress T hk hdis m hcap hpos hgrowth σ hσ hspread
intro hp1 state hrank
have hp : 0 < Real.exp 50 * (4 * σ) := by positivity
have hgood := reduction_good_probability_ge hp hp1 state.capacity
(fun i => capacityReserve σ (state.capacity i)) state.tree
state.disjoint state.capacities state.spread state.positive
(fun i _ => (capacityReserve_pos hσ (state.capacity i)).le)
(fun i _ => capacityReserve_div_sampling_le hσ (state.capacity i)) state.growth
have hmono := (bernoulliLaw (X := X) (Real.exp 50 * (4 * σ)) hp.le hp1.le).prob_mono
(P := fun W => Good (Real.exp 50 * (4 * σ)) state.capacity W state.tree)
(Q := fun W => ∃ next, state.Advances W next)
(fun W hW => state.exists_advance_of_good W hσ hp hrank hW)
exact hgood.trans hmono
end LeanBlast.SecondKahnKalai
end
end OAI