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23773
\section{Non-Zero Natural Numbers under Multiplication form Commutative Monoid} Tags: Natural Numbers, Examples of Monoids, Monoid Examples, Examples of Commutative Monoids \begin{theorem} Let $\N_{>0}$ be the set of natural numbers without zero, i.e. $\N_{>0} = \N \setminus \set 0$. The structure $\struct{\N_{>0}, \t...
23774
\section{Non-Zero Rational Numbers Closed under Multiplication} Tags: Algebraic Closure, Rational Multiplication, Rational Numbers \begin{theorem} The set of non-zero rational numbers is closed under multiplication. \end{theorem} \begin{proof} Recall that Rational Numbers form Field under the operations of addition a...
23775
\section{Non-Zero Rational Numbers under Multiplication form Infinite Abelian Group} Tags: Abelian Groups, Examples of Abelian Groups, Group Examples, Abelian Groups: Examples, Infinite Groups: Examples, Rational Multiplication, Examples of Infinite Groups, Abelian Group Examples, Rational Numbers \begin{theorem} Let ...
23776
\section{Non-Zero Real Numbers Closed under Multiplication} Tags: Real Numbers, Algebraic Closure, Non-Zero Real Numbers Closed under Multiplication, Real Multiplication \begin{theorem} The set of non-zero real numbers is closed under multiplication: :$\forall x, y \in \R_{\ne 0}: x \times y \in \R_{\ne 0}$ \end{theor...
23777
\section{Non-Zero Real Numbers under Multiplication form Abelian Group} Tags: Non-Zero Real Numbers under Multiplication form Abelian Group, Abelian Groups, Examples of Abelian Groups, Group Examples, Abelian Groups: Examples, Real Numbers, Infinite Groups: Examples, Examples of Infinite Groups, Abelian Group Examples,...
23778
\section{Non-Zero Value of Continuous Real-Valued Function has Neighborhood not including Zero} Tags: Continuous Mappings on Metric Spaces \begin{theorem} Let $M = \struct {A, d}$ be a metric space. Let $f: M \to \R$ be a continuous real-valued function. Let $\map f a > 0$ for some $a \in M$. Then there exists $\delta...
23779
\section{Nonconstant Periodic Function with no Period is Discontinuous Everywhere} Tags: Periodic Functions \begin{theorem} Let $f$ be a real periodic function that does not have a period. Then $f$ is either constant or discontinuous everywhere. \end{theorem} \begin{proof} Let $f$ be a real periodic function that doe...
23780
\section{Nonempty Grothendieck Universe contains Von Neumann Natural Numbers} Tags: Set Theory, Grothendieck Universes \begin{theorem} Let $\mathbb U$ be a non-empty Grothendieck universe. Let $\N$ denote the set of von Neumann natural numbers. Then $\N$ is a subset of $\mathbb U$. \end{theorem} \begin{proof} We prov...
23781
\section{Nonlimit Ordinal Cofinal to One} Tags: Ordinals \begin{theorem} Let $x$ be a nonlimit non-empty ordinal. Let $\operatorname{cof}$ denote the cofinal relation. Let $1$ denote the ordinal one. Then: :$\operatorname{cof} \left({x, 1}\right)$ \end{theorem} \begin{proof} Since $1 = 0^+$, $1$ is not a limit ordin...
23782
\section{Nonnegative Quadratic Functional implies no Interior Conjugate Points} Tags: Calculus of Variations \begin{theorem} If the quadratic functional :$\ds \int_a^b \paren {P h'^2 + Q h^2} \rd x$ where: :$\forall x \in \closedint a b: \map P x > 0$ is nonnegative for all $\map h x$: :$\map h a = \map h b = 0$ then...
23783
\section{Nontrivial Zeroes of Riemann Zeta Function are Symmetrical with respect to Critical Line} Tags: Riemann Zeta Function \begin{theorem} The nontrivial zeroes of the Riemann $\zeta$ function are distributed symmetrically {{WRT}} the critical line. That is, suppose $s_1 = \sigma_1 + i t$ is a nontrivial zero of ...
23784
\section{Nonzero Ideal of Polynomial Ring over Field has Unique Monic Generator} Tags: Polynomial Rings \begin{theorem} Let $K$ be a field. Let $K \sqbrk x$ be the polynomial ring in one variable over $K$. Let $I \subseteq K \sqbrk x$ be a nonzero ideal. Then $I$ is generated by a unique monic polynomial. \end{theorem...
23785
\section{Nonzero natural number is another natural number successor} Tags: Natural Numbers, Proofs by Induction \begin{theorem} Let $\N$ be the 0-based natural numbers: :$\N = \left\{{0, 1, 2, \ldots}\right\}$ Let $s: \N \to \N: \map s n = n + 1$ be the successor function. Then: :$\forall n \in \N \setminus \set 0 \pa...
23786
\section{Norm Sequence of Cauchy Sequence has Limit} Tags: Cauchy Sequences, Normed Division Rings \begin{theorem} Let $\struct {R, \norm {\, \cdot \,} }$ be a normed division ring. Let $\sequence {x_n}$ be a Cauchy sequence in $R$. Then $\sequence {\norm {x_n} }$ has a limit in $\R$. That is, :$\exists l \in \R: \ds ...
23787
\section{Norm is Complete Iff Equivalent Norm is Complete} Tags: Normed Division Rings, Complete Metric Spaces \begin{theorem} Let $R$ be a division ring. Let $\norm {\,\cdot\,}_1$ and $\norm {\,\cdot\,}_2$ be equivalent norms on $R$. Then: :$\struct {R,\norm {\,\cdot\,}_1}$ is complete {{iff}} $\struct {R,\norm {\,\c...
23788
\section{Norm is Continuous} Tags: Continuity, Norm Theory, Continuous Mappings \begin{theorem} Let $\struct {V, \norm {\,\cdot\,} }$ be a normed vector space. Then the mapping $x \mapsto \norm x$ is continuous. Here, the metric used is the metric $d$ induced by $\norm {\,\cdot\,}$. \end{theorem} \begin{proof} Since ...
23789
\section{Norm of Adjoint} Tags: Adjoints \begin{theorem} Let $H, K$ be Hilbert spaces. Let $A \in \map B {H, K}$ be a bounded linear transformation. Then the norm of $A$ satisfies: :$\norm A^2 = \norm {A^*}^2 = \norm {A^* A}$ where $A^*$ denotes the adjoint of $A$. \end{theorem} \begin{proof} Let $h \in H$ such that ...
23790
\section{Norm of Eisenstein Integer} Tags: Number Theory, Complex Analysis, Algebraic Number Theory \begin{theorem} Let $\alpha$ be an Eisenstein integer. That is, $\alpha = a + b \omega$ for some $a, b \in \Z$, where $\omega = e^{2\pi i /3}$. Then: :$\cmod \alpha^2 = a^2 - a b + b^2$ where $\cmod {\, \cdot \,}$ denot...
23791
\section{Norm of Hermitian Operator} Tags: Adjoints, Definitions: Adjoints \begin{theorem} Let $\mathbb F \in \set {\R, \C}$. Let $\HH$ be a Hilbert space over $\mathbb F$. Let $A : \HH \to \HH$ be a bounded Hermitian operator. Let $\innerprod \cdot \cdot_\HH$ denote the inner product on $\HH$. Let $\norm \cdot_\HH$ ...
23792
\section{Norm of Unit of Normed Division Algebra} Tags: Norm Theory, Algebras \begin{theorem} Let $\struct {A_F, \oplus}$ be a normed division algebra. Let the unit of $\struct {A_F, \oplus}$ be $1_A$. Then: :$\norm {1_A} = 1$ where $\norm {1_A}$ denotes the norm of $1_A$. \end{theorem} \begin{proof} By definition: :...
23793
\section{Norm of Vector Cross Product} Tags: Vector Cross Product, Vector Algebra \begin{theorem} Let $\mathbf a$ and $\mathbf b$ be vectors in the Euclidean space $\R^3$. Let $\times$ denote the vector cross product. Then: :$(1): \quad$ $\left\Vert{ \mathbf a \times \mathbf b }\right\Vert^2 = \left\Vert{\mathbf a}\ri...
23794
\section{Norm on Bounded Linear Functional is Finite} Tags: Hilbert Spaces \begin{theorem} Let $H$ be a Hilbert space. Let $L$ be a bounded linear functional on $H$. Let $\norm L$ denote the norm on $L$ defined as: :$\norm L = \inf \set {c > 0: \forall h \in H: \size {L h} \le c \norm h_H}$ Then: :$\norm L < \infty$ \...
23795
\section{Norm on Bounded Linear Transformation is Finite} Tags: Hilbert Spaces \begin{theorem} Let $H, K$ be Hilbert spaces. Let $A: H \to K$ be a bounded linear transformation. Let $\norm A$ denote the norm of $A$ defined by: :$\norm A = \inf \set {c > 0: \forall h \in H: \norm {A h}_K \le c \norm h_H}$ Then: :$\norm...
23796
\section{Norm on Bounded Linear Transformation is Submultiplicative} Tags: Linear Transformations on Hilbert Spaces, Bounded Linear Transformations \begin{theorem} Let $\struct {X, \norm \cdot_X}$, $\struct {Y, \norm \cdot_Y}$ and $\struct {Z, \norm \cdot_Z}$ be normed vector spaces. Let $A : X \to Y$ and $B : Y \to Z...
23797
\section{Norm on Vector Space is Continuous Function} Tags: Norm Theory \begin{theorem} Let $V$ be a vector space with norm $\norm {\, \cdot \,}$. The function $\norm {\, \cdot \,}: V \to \R$ is continuous. \end{theorem} \begin{proof} Let $x_n \to x$ in $V$. We have: :$x_n \to x \implies \norm {x_n - x} \to 0$ By the...
23798
\section{Norm satisfying Parallelogram Law induced by Inner Product} Tags: Normed Vector Spaces, Inner Product Spaces, Norm satisfying Parallelogram Law induced by Inner Product \begin{theorem} Let $V$ be a vector space over $\R$. Let $\norm \cdot : V \to \R$ be a norm on $V$ such that: :$\norm {x + y}^2 + \norm {x -...
23799
\section{Normal Space is Preserved under Homeomorphism} Tags: Separation Axioms, Normal Spaces \begin{theorem} Let $T_A = \struct {S_A, \tau_A}$ and $T_B = \struct {S_B, \tau_B}$ be topological spaces. Let $\phi: T_A \to T_B$ be a homeomorphism. If $T_A$ is a normal space, then so is $T_B$. \end{theorem} \begin{proof...
23800
\section{Nicely Normed Cayley-Dickson Construction from Associative Algebra is Alternative} Tags: Cayley-Dickson Construction \begin{theorem} Let $A = \left({A_F, \oplus}\right)$ be a $*$-algebra. Let $A' = \left({A_F, \oplus'}\right)$ be constructed from $A$ using the Cayley-Dickson construction. Then $A'$ is a nicel...
23801
\section{Niemytzki Plane is Topology} Tags: Niemytzki Plane \begin{theorem} Niemytzki plane is a topological space. \end{theorem} \begin{proof} By definition $T = \struct {S, \tau}$ is the Niemytzki plane {{iff}}: {{begin-eqn}} {{eqn | n = 1 | l = S | r = \set {\tuple {x, y}: y \ge 0} }} {{eqn | n = 2 ...
23802
\section{Nilpotent Element is Zero Divisor} Tags: Nilpotent Ring Elements, Zero Divisors, Ring Theory \begin{theorem} Let $\struct {R, +, \circ}$ be a ring whose zero is $0_R$. Suppose further that $R$ is not the null ring. Let $x \in R$ be a nilpotent element of $R$. Then $x$ is a zero divisor in $R$. \end{theorem} ...
23803
\section{Nilpotent Elements of Commutative Ring form Ideal} Tags: Nilpotent Ring Elements, Ring Theory, Ideal Theory, Commutative Rings \begin{theorem} Let $\struct {R, +, \circ}$ be a commutative ring whose zero is $0_R$ and whose unity is $1_R$. The subset of nilpotent elements of $R$ form an ideal of $R$. \end{theo...
23804
\section{Nilpotent Ring Element plus Unity is Unit} Tags: Nilpotence \begin{theorem} Let $A$ be a ring with unity. Let $1 \in A$ be its unity. Let $a \in A$ be nilpotent. Then $1 + a$ is a unit of $A$. \end{theorem} \begin{proof} Because $a$ is nilpotent, there exists a natural number $n > 0$ with $a^n = 0$. By Sum o...
23805
\section{Nine Regular Polyhedra} Tags: Regular Polyhedra \begin{theorem} There exist $9$ regular polyhedra. \end{theorem} \begin{proof} From Five Platonic Solids, there exist $5$ regular polyhedra which are convex: :the regular tetrahedron :the cube :the regular octahedron :the regular dodecahedron :the regular icosa...
23806
\section{Niven's Theorem} Tags: Trigonometry, Niven's Theorem \begin{theorem} Consider the angles $\theta$ in the range $0 \le \theta \le \dfrac \pi 2$. The only values of $\theta$ such that both $\dfrac \theta \pi$ and $\sin \theta$ are rational are: :$\theta = 0: \sin \theta = 0$ :$\theta = \dfrac \pi 6: \sin \theta...
23807
\section{Niven's Theorem/Lemma} Tags: Proofs by Induction, Niven's Theorem \begin{theorem} For any integer $n \ge 1$, there exists a polynomial $\map {F_n} x$ such that: :$\map {F_n} {2 \cos t} = 2 \cos n t$ In addition: :$\deg F_n = n$ and $F_n$ is a monic polynomial with integer coefficients. \end{theorem} \begin{p...
23808
\section{No 4 Fibonacci Numbers can be in Arithmetic Sequence} Tags: Arithmetic Progressions, Arithmetic Sequences, Fibonacci Numbers \begin{theorem} Let $a, b, c, d$ be distinct Fibonacci numbers. Then, except for the trivial case: :$a = 0, b = 1, c = 2, d = 3$ it is not possible that $a, b, c, d$ are in arithmetic s...
23809
\section{No Bijection between Finite Set and Proper Subset} Tags: Set Theory, No Bijection between Finite Set and Proper Subset, Subsets, Subset \begin{theorem} A finite set can not be in one-to-one correspondence with one of its proper subsets. That is, a finite set is not Dedekind-infinite. \end{theorem} \begin{pro...
23810
\section{No Bijection from Set to its Power Set} Tags: Bijections, Power Set, Mappings \begin{theorem} Let $S$ be a set. Let $\powerset S$ denote the power set of $S$. There is no bijection $f: S \to \powerset S$. \end{theorem} \begin{proof} A bijection is by its definition also a surjection. By Cantor's Theorem ther...
23811
\section{No Boolean Interpretation Models a WFF and its Negation} Tags: Propositional Logic, Propositional Calculus \begin{theorem} Let $v$ be a boolean interpretation. Let $\mathbf A$ be a WFF of propositional logic. Then $v$ can not model both $\mathbf A$ and $\neg \mathbf A$. \end{theorem} \begin{proof} Suppose th...
23812
\section{No Group has Two Order 2 Elements} Tags: Group Theory, Order of Group Elements \begin{theorem} A group can not contain exactly two elements of order $2$. \end{theorem} \begin{proof} Let $\struct {G, \circ}$ be a group whose identity is $e$. Suppose: : $s, t \in \struct {G, \circ}\: s \ne t, \order s = \order...
23813
\section{No Infinitely Descending Membership Chains} Tags: Set Theory \begin{theorem} Let $\omega$ denote the minimal infinite successor set. Let $F$ be a function whose domain is $\omega$. Then: :$\exists n \in \omega: \map F {n^+} \notin \map F n$ \end{theorem} \begin{proof} Let $F$ be a function whose domain is $\...
23814
\section{No Infinitely Descending Membership Chains/Corollary} Tags: Axiom of Foundation \begin{theorem} There cannot exist a sequence $\sequence {x_n}$ whose domain is $\N_{\gt 0}$ such that: :$\forall n \in \N_{\gt 0}: x_{n+1} \in x_n$ \end{theorem} \begin{proof} {{AimForCont}} there is a sequence like that. From t...
23815
\section{No Injection from Power Set to Set} Tags: Power Set, No Injection from Power Set to Set, Injections \begin{theorem} Let $S$ be a set. Let $\powerset S$ be the power set of $S$. Then there is no injection from $\powerset S$ into $S$. \end{theorem} \begin{proof} The identity mapping $f: \mathcal P(S) \to \math...
23816
\section{No Injection from Power Set to Set/Lemma} Tags: Power Set, No Injection from Power Set to Set \begin{theorem} Let $S$ be a set. Let $\powerset S$ be the power set of $S$. Then there does not exist a set $B$ such that there is an injection from $B$ into $S$ and a surjection from $B$ onto $\powerset S$. \end{th...
23817
\section{No Isomorphism from Woset to Initial Segment} Tags: Order Isomorphisms, Well-Orderings, Orderings, Order Morphisms \begin{theorem} Let $\struct {S, \preceq}$ be a woset. Let $a \in S$, and let $S_a$ be the initial segment of $S$ determined by $a$. Then there is no order isomorphism between $S$ and $S_a$. \end...
23818
\section{No Largest Ordinal} Tags: Ordinals \begin{theorem} Let $a$ be a set of ordinals. Then: :$\forall x \in a: x \prec \paren {\bigcup a}^+$ \end{theorem} \begin{proof} For this proof, we shall use $\prec$, $\in$, and $\subset$ interchangeably. We are justified in doing this because of Ordering on Ordinal is Subs...
23819
\section{No Membership Loops} Tags: Set Theory, Class Theory, Axiom of Foundation, Axiom of Regularity \begin{theorem} For any proper classes or sets $A_1, A_2, \ldots, A_n$: :$\neg \paren {A_1 \in A_2 \land A_2 \in A_3 \land \cdots \land A_n \in A_1}$ \end{theorem} \begin{proof} {{NotZFC}} Either $A_1, A_2, \ldots, ...
23820
\section{No Natural Number between Number and Successor} Tags: Ordinals, No Ordinal Between Set and Successor, Ordering on Natural Numbers, No Natural Number between Number and Successor \begin{theorem} Let $\N$ be the natural numbers. Let $n \in \N$. Then no natural number $m$ exists strictly between $n$ and its succ...
23821
\section{No Non-Trivial Norm on Rational Numbers is Complete} Tags: Normed Division Rings, Complete Metric Spaces \begin{theorem} No non-trivial norm on the set of the rational numbers is complete. \end{theorem} \begin{proof} By P-adic Norm not Complete on Rational Numbers, no $p$-adic norm $\norm{\,\cdot\,}_p$ on th...
23822
\section{No Order Isomophism Between Distinct Initial Segments of Woset} Tags: Well-Orderings \begin{theorem} Let $E$ be a well-ordered set. Let $S_\alpha, S_\beta$ be initial segments of $E$ that are order isomorphic. Then $S_\alpha = S_\beta$. \end{theorem} \begin{proof} {{AimForCont}} $S_\alpha \ne S_\beta$. Then ...
23823
\section{No Quadruple of Consecutive Sums of Squares Exists} Tags: Sums of Squares \begin{theorem} It is not possible for a quadruple of consecutive positive integers each of which is the sum of two squares. \end{theorem} \begin{proof} $4$ consecutive positive integers will be in the forms: {{begin-eqn}} {{eqn | l = ...
23824
\section{No Simple Graph is Perfect} Tags: Simple Graphs, Graph Theory, Perfect Graphs \begin{theorem} Let $G$ be a simple graph whose order is $2$ or greater. Then $G$ is not perfect. \end{theorem} \begin{proof} Recall that a perfect graph is one where each vertex is of different degree. We note in passing that the ...
23825
\section{No Valid Categorical Syllogism contains two Particular Premises} Tags: Categorical Syllogisms \begin{theorem} Let $Q$ be a valid categorical syllogism. Then at least one of the premises of $Q$ is universal. \end{theorem} \begin{proof} Suppose both premises of $Q$ are particular. Then the pattern of $Q$ is on...
23826
\section{No Valid Categorical Syllogism with Particular Premise has Universal Conclusion} Tags: Categorical Syllogisms \begin{theorem} Let $Q$ be a valid categorical syllogism. Let one of the premises of $Q$ be particular. Then the conclusion of $Q$ is also particular. \end{theorem} \begin{proof} Let the major premis...
23827
\section{Noether's Theorem (Calculus of Variations)} Tags: Physics, Partial Differential Equations, Calculus of Variations \begin{theorem} Let $y_i$, $F$, $\Psi_i$, $\Phi$ be real functions. Let $x, \epsilon \in \R$. Let $\mathbf y = \sequence {y_i}_{1 \mathop \le i \mathop \le n}$ and $\mathbf \Psi = \sequence{\Psi_i...
23828
\section{Noether's Theorem (Hamiltonian Mechanics)} Tags: Physics, Partial Differential Equations, Calculus of Variations, Hamiltonian Mechanics \begin{theorem} Let there be an infinitesimal transformation of generalised coordinates such that: :$q_i \to \tilde q_i = q_i + q_i^\alpha \tuple{q, \dot q, t} \varepsilon_\a...
23829
\section{Noether Normalization Lemma} Tags: Commutative Algebra, Named Theorems \begin{theorem} Let $k$ be a field. Let $A$ be a non-trivial finitely generated $k$-algebra. {{explain|the above link is for Definition:Non-Trivial Ring -- we need to define a Definition:Non-Trivial Algebra}} Then there exists $n \in \N$ a...
23830
\section{Noetherian Domain is Factorization Domain} Tags: Factorization, Ring Theory \begin{theorem} Let $R$ be a noetherian integral domain. Then $R$ is a factorization domain. \end{theorem} \begin{proof} Let $\FF$ be the set of ideals of $R$ of the form $x R$, with $x$ not a unit and such that $x$ cannot be decompo...
23831
\section{Noetherian Space is Compact} Tags: Noetherian Spaces \begin{theorem} Let $\struct {X, \tau}$ be a Noetherian topological space. Then $\struct {X, \tau}$ is compact. \end{theorem} \begin{proof} {{tidy}} Let $\family {U_i}_{i \mathop \in I}$ be a cover of $X$. That is, $\bigcup_{i \mathop \in I} U_i = X$. Let ...
23832
\section{Non-Abelian Group of Order p Cubed has Exactly One Normal Subgroup of Order p} Tags: P-Groups \begin{theorem} Let $p$ be a prime number. Let $G$ be a non-abelian group of order $p^3$. Then $G$ contains exactly one normal subgroup of order $p$. \end{theorem} \begin{proof} From Center of Group of Prime Power O...
23833
\section{Non-Abelian Order 10 Group has Order 5 Element} Tags: Non-Abelian Order 10 Group has Order 5 Element, Groups of Order 10, Order of Group Elements \begin{theorem} Let $G$ be a non-abelian group of order $10$. Then $G$ has at least one element of order $5$. \end{theorem} \begin{proof} By Lagrange's Theorem, al...
23834
\section{Non-Abelian Order 2p Group has Order p Element} Tags: Order of Group Elements, Groups of Order 2 p \begin{theorem} Let $p$ be an odd prime. Let $G$ be a non-abelian group of order $2 p$. Then $G$ has at least one element of order $p$. \end{theorem} \begin{proof} By Lagrange's Theorem, all the elements of $G$...
23835
\section{Non-Abelian Order 8 Group has Order 4 Element} Tags: Groups of Order 8 \begin{theorem} Let $G$ be a non-abelian group of order $8$. Then $G$ has at least one element of order $4$. \end{theorem} \begin{proof} Let $e \in G$ be the identity of $G$. Let $g \in G$ be an arbitrary element of $G$ such that $g \ne e...
23836
\section{Non-Abelian Order 8 Group with One Order 2 Element is Quaternion Group} Tags: Quaternion Group, Non-Abelian Order 8 Group with One Order 2 Element is Quaternion Group, Groups of Order 8 \begin{theorem} Let $G$ be a group with the following properties: :$(1): \quad G$ is non-abelian. :$(2): \quad G$ is of orde...
23837
\section{Non-Abelian Simple Finite Groups are Infinitely Many} Tags: Simple Groups \begin{theorem} There exist infinitely many types of group which are non-abelian and finite. \end{theorem} \begin{proof} We have that Alternating Group is Simple except on 4 Letters. So for all $n \in \N$ such that $n \ne 4$, the alter...
23838
\section{Non-Archimedean Division Ring Iff Non-Archimedean Completion} Tags: Complete Metric Spaces, Definitions: Norm Theory, Division Rings, Normed Division Rings, Definitions: Division Rings, Norm Theory, Definitions: Complete Metric Spaces, Non-Archimedean Norms \begin{theorem} Let $\struct {R, \norm {\, \cdot \,}...