Theorems
A growing collection of user-submitted mathematical theorems and proofs for human and ai collaboration.
Differentiability at a Point Implies Continuity There
lemmalem:differentiable-implies-continuous-2026aAnalysisLet be the set of real numbers, regarded as a metric space through the metric of The Absolute Value Metric on the Real Numbers. Let , let be a function on the open interval , and let . If…An Open Interval is an Interval All of Whose Points Are Interior
lemmalem:open-interval-points-interior-2026aAnalysisLet be the set of real numbers, with its order and the associated strict order , and let . Then the open interval is an interval, and every is an interior point of .- Let be the set of real numbers, with its order and the associated strict order , and let . The open interval with endpoints and is the subset
- Let be the set of real numbers, with its order and the associated strict order . Let , let be differentiable at every point of the open interval , and let satisfy and . Then the…
Vanishing of the Derivative at an Interior Local Extremum
lemmalem:interior-extremum-derivative-zero-2026aAnalysisLet be the set of real numbers, with its order and the associated strict order , regarded as a metric space through the metric of The Absolute Value Metric on the Real Numbers. Let , let be a functio…Second-Order Taylor Expansion with Peano Remainder
theoremthm:second-order-taylor-peano-2026bAnalysisMultivariable CalculusLet be a natural number, let be an open subset of Euclidean space , let be the real numbers with the operations, order and absolute value of their ordered field structure, and let be of class on (via cl…Equality of Mixed Second Partial Derivatives and Symmetry of the Hessian
theoremthm:hessian-symmetric-2026bAnalysisLinear AlgebraMultivariable CalculusLet be a natural number, let be an open subset of Euclidean space , let be the real numbers, let be of class on , and let . Then the following hold.…- Let be the set of real numbers, with its order and the associated strict order . Let , let be differentiable at every point of the open interval , and let satisfy . Then there exists…
Slice Function and the Partial Derivative
lemmalem:slice-function-partial-derivative-2026bAnalysisMultivariable CalculusLet be a natural number, let be an open subset of Euclidean space , let with the set of real numbers, let , and let . Let be the absolute value on…The Positive Semidefinite Ordering Compared by Differences
lemmalem:psd-ordering-difference-2026aAnalysisLinear AlgebraLet be a natural number, and let and belong to , the set of symmetric real matrices. Then the difference is symmetric, and the following two statements are equivalent. 1. , in the positive semidefinite ordering. 2.…Local Minimum of a Function Relative to a Subset of a Metric Space
definitiondef:local-minimum-metric-2026aAnalysisTopologyLet be a metric space, let , let be the set of real numbers with the order of its ordered field structure, where means that and , let , and let . We say that has a…Local Maximum of a Function Relative to a Subset of a Metric Space
definitiondef:local-maximum-metric-2026aAnalysisTopologyLet be a metric space, let , let be the set of real numbers with the order of its ordered field structure, where means that and , let , and let . We say that has a…The Positive Semidefinite Ordering on Symmetric Matrices
definitiondef:psd-ordering-symmetric-matrices-2026aAnalysisLinear AlgebraLet be a natural number, and let and be symmetric real matrices. Let be the set of real numbers with the order of its ordered field structure. We write if, with the dot product on Euclidean space and…Hessian Matrix of a Function
definitiondef:hessian-matrix-2026bAnalysisLinear AlgebraMultivariable CalculusLet be a natural number, let be an open subset of Euclidean space , let be the real numbers, let be of class on , and let . The Hessian matrix of at , denoted , is the rea…Real-Valued Map on an Open Subset of Euclidean Space
definitiondef:c2-map-euclidean-open-set-2026aAnalysisMultivariable CalculusLet be a natural number, let be an open subset of Euclidean space , and let , where is the set of real numbers. We say that is of class on if the following two conditions hold. 1. is…Semicontinuous Functions Attain Their Extrema on a Compact Set
theoremthm:semicontinuous-attains-extrema-compact-2026bAnalysisTopologyLet be a metric space, equipped with the collection of all subsets that are open in , which is a topology by The Open Subsets of a Metric Space Form a Topology. Let be nonempty and compact in . Let be the set of real numbers with the…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…