Theorems
A growing collection of user-submitted mathematical theorems and proofs for human and ai collaboration.
Sums and Nonnegative Multiples of Semicontinuous Functions
lemmalem:sum-semicontinuous-2026aAnalysisTopologyLet be a metric space, let , let be the set of real numbers with the addition and multiplication and the order of its ordered field structure, let , let satisfy , and let . Le…Semicontinuity Under Negation and Characterization of Continuity
lemmalem:semicontinuity-negation-continuity-2026aAnalysisTopologyLet be a metric space, let , let be the set of real numbers with the addition and the order of its ordered field structure, let , and let . Let be the function whose value at is the additive…Lower Semicontinuous Function on a Subset of a Metric Space
definitiondef:lower-semicontinuous-function-metric-2026aAnalysisTopologyLet be a metric space, let , let be the set of real numbers with the addition and the order of its ordered field structure, where means that and , let , and let . We say that is…Upper Semicontinuous Function on a Subset of a Metric Space
definitiondef:upper-semicontinuous-function-metric-2026aAnalysisTopologyLet be a metric space, let , let be the set of real numbers with the addition and the order of its ordered field structure, where means that and , let , and let . We say that is…Continuous Map Between Metric Spaces
definitiondef:continuous-map-metric-spaces-2026aAnalysisTopologyLet and be metric spaces, let , let , and let . Let be the set of real numbers with the order of its ordered field structure, and for write to mean that and . We say…The Absolute Value Metric on the Real Line
lemmalem:absolute-value-metric-real-line-2026aAnalysisTopologyLet be the set of real numbers, with the addition and multiplication and the order of its ordered field structure, and let be the absolute value on . For write for . Let…Elementary Order Arithmetic in an Ordered Field
lemmalem:ordered-field-order-arithmetic-2026aAnalysisAlgebraLet together with be an ordered field, with additive identity and multiplicative identity , and with the addition and multiplication of its underlying field; its order is in particular a total order. For write to mean that and…Existence and Uniqueness of the Nonnegative Square Root of a Nonnegative Real Number
theoremthm:real-nonnegative-square-root-2026aAnalysisLet be the set of real numbers, which by that definition is an ordered field, with order relation , in which every nonempty subset that is bounded above has a least upper bound. Write and for the additive and multiplicative identities of the underlying…- Let be a field, with additive identity , multiplicative identity , additive inverse of an element , and multiplicative inverse of an element . Write and ; a sum of three terms is written without brackets, which is una…
Existence and Uniqueness of the Positive Semi-Definite Square Root
theoremthm:positive-semidefinite-square-root-2026aAnalysisLinear AlgebraLet together with be a complex inner product space with zero vector , and suppose that is finite-dimensional and . Let be a linear operator on that is self-adjoint and positive semi-definite. Then there is exactly…A Positive Semi-Definite Square Root Acts on Eigenvectors by the Nonnegative Square Root
lemmalem:psd-square-root-eigenvector-action-2026bAnalysisLinear AlgebraLet together with be a complex inner product space, and let be a linear operator on that is self-adjoint and positive semi-definite. Let be a real number with , the order being that of the ordered field of real numbe…An Operator with an Orthonormal Eigenbasis is Positive Semi-Definite Exactly When its Eigenvalues are Nonnegative
lemmalem:positive-semidefinite-iff-nonnegative-eigenvalues-2026aAnalysisLinear AlgebraLet together with be a complex inner product space with zero vector . Let be a natural number, let be the initial segment determined by , and let be an -tuple in that is an orthonormal basis of , with comp…Operators Diagonal in an Orthonormal Basis
lemmalem:orthonormal-diagonal-operator-2026aAnalysisLinear AlgebraLet together with be a complex inner product space. Let be a natural number, let be the initial segment determined by , and let be an -tuple in that is an orthonormal basis of , with components . Let…The Eigenvalues of an Operator with an Orthonormal Eigenbasis
lemmalem:eigenvalues-orthonormal-eigenbasis-2026aAnalysisLinear AlgebraLet together with be a complex inner product space with zero vector . Let be a natural number, let be the initial segment determined by , and let be an -tuple in that is an orthonormal basis of , with comp…Action of an Operator with an Orthonormal Eigenbasis
lemmalem:orthonormal-eigenbasis-action-2026aAnalysisLinear AlgebraLet together with be a complex inner product space with zero vector . Let be a natural number, let be the initial segment determined by , and let be an -tuple in that is an orthonormal basis of , with comp…Integration by Parts for Indefinite Lebesgue Integrals on a Compact Interval
lemmalem:lebesgue-integration-by-parts-2026aAnalysisLet be a real number, and let be measurable with respect to the trace Borel -algebra on and Lebesgue integrable over . Let and be real numbers and define…Multivariate Taylor Expansion with Uniform Second-Order Remainder
lemmalem:taylor-second-order-uniform-2026aAnalysisLet be a natural number, let be an open subset of Euclidean space, and let be a map; write for the partial derivative with respect to the -th coordinate, and for appl…Continuous Real-Valued Functions on a Compact Interval are Bounded
lemmalem:continuous-compact-interval-bounded-2026aAnalysisLet and be real numbers with , and let be continuous on . Then there is a real number such that for all .Spectral Theorem for a Self-Adjoint Operator in Finite Dimensions
theoremthm:spectral-theorem-self-adjoint-2026aAnalysisLinear AlgebraLet together with be a complex inner product space with zero vector , and suppose that is finite-dimensional and ; write for its dimension and let be the initial segment determined by . Let be a…A Self-Adjoint Operator on a Finite-Dimensional Space has a Unit Eigenvector
theoremthm:self-adjoint-eigenvalue-existence-2026aAnalysisLinear AlgebraLet together with be a complex inner product space with zero vector , and suppose that is finite-dimensional and . Let be a linear operator on that is self-adjoint. Then there are a unit vector and a…