Theorems
A growing collection of user-submitted mathematical theorems and proofs for human and ai collaboration.
Euclidean Continuity Agrees with Metric Continuity for Real-Valued Functions
lemmalem:euclidean-metric-continuity-agree-2026aAnalysisTopologyMultivariable CalculusLet be a natural number, let be a subset of Euclidean space , let be the set of real numbers with the operations and the order of its ordered field structure, where for we write to mean that…Independence Fubini: Integration in an Independent Random Vector Given a Sub-Sigma-Algebra
lemmalem:independence-fubini-2026aAnalysisProbabilityLet be a probability space, let be a -algebra on with , let be a natural number, and let be measurable with respect to and the -fold…Cumulative-Rate Time Change: Regularity, Substitution, and Crossing Times
lemmalem:cumulative-rate-substitution-2026bAnalysisLet and be real numbers and let be measurable with respect to the trace Borel -algebra . Define the cumulative rate by the…Uniqueness of Finite Measures on a Generating Pi-System and the Density of the Exponential Law
lemmalem:finite-measure-uniqueness-2026aAnalysisProbability(Uniqueness) Let be a measurable space, let be a -system of subsets of whose generated -algebra is , and let and be measures on with and for every…- Let be a natural number and let be a real number. Write and for the -fold Borel -algebra and product Lebesgue measure on , and for the factorial. The ordered time simplex with horizon is t…
Assembly of Measure Spaces: Restriction, Transport, One-Point Spaces, and Countable Disjoint Unions
lemmalem:measure-space-assembly-2026aAnalysisMeasurability of maps between measurable spaces is that of Measurable Function and Real-Valued Measurable Function; measurability and integrals of -valued functions are those of Lebesgue Integral of a Nonnegative Measurable Function; measures use the conventions of…Finite Products of Lebesgue Measure and Coordinate Integration on
lemmalem:lebesgue-product-coordinate-integration-2026aAnalysisProbabilityLet be a natural number. Write for the Borel -algebra on the real numbers and for Lebesgue measure on it. Members of the -fold Cartesian product are written as tuples , and f…Image Measures, Measures with Densities, and Change of Variables
lemmalem:image-measure-density-2026aAnalysisProbabilityLet be a measure space and let be a measurable space. Measurability of maps between measurable spaces is that of Measurable Function and Real-Valued Measurable Function; measurability and integrals of -valued functions are those…- A function of class is a classical solution when vanishes at its own value, gradient and Hessian at every point.
Classical Subsolution and Supersolution of a Second-Order Equation
definitiondef:classical-sub-supersolution-2026cAnalysisPDEA function of class is a classical subsolution if pointwise at its own derivatives, and a classical supersolution if .- Let be a natural number, let be an open subset of Euclidean space , let be the set of real numbers with the order of its ordered field structure, let be the…
Degenerate Elliptic Second-Order Equation Operator
definitiondef:degenerate-elliptic-operator-2026aAnalysisPDELet be a natural number, let be an open subset of Euclidean space , let be the set of real numbers with the order of its ordered field structure, let be the…Second-Order Equation Operator on a Euclidean Open Set
definitiondef:second-order-equation-operator-2026aAnalysisPDELet be a natural number, let be an open subset of Euclidean space , let be the set of real numbers, and let be the set of symmetric real matrices. We write…Gradient of a Real-Valued Function on a Euclidean Open Set
definitiondef:gradient-euclidean-open-set-2026bAnalysisMultivariable CalculusLet be a natural number, let be an open subset of Euclidean space , let be the set of real numbers, let , and let . Assume that for every the partial derivative of with respe…Monotonicity of Squaring on the Nonnegative Elements of an Ordered Field
lemmalem:squares-monotone-nonnegative-2026aAnalysisAlgebraLet together with be an ordered field, with additive identity , and for let denote the associated strict order, that is, together with . For write for . Let satisfy…- Let be a natural number, let be the real numbers, let be an open subset of Euclidean space , and let , regarded where a map into a Euclidean space is required as the map into whose single coordinate function…
A Real-Valued Function is Differentiable at Every Point
theoremthm:c1-implies-differentiable-2026bAnalysisMultivariable CalculusLet be a natural number, let be an open subset of Euclidean space , let be a real-valued function, regarded also as a map into with single coordinate function , and let . Suppose that is…The Euclidean Distance on the Real Line is the Absolute Value Metric
lemmalem:euclidean-distance-real-line-2026bAnalysisTopologyLet be the set of real numbers, let be the absolute value on , let be the metric of The Absolute Value Metric on the Real Numbers, and let be the Euclidean distance on in the case , with…- Let be a set equipped with a total order . For we write to mean that and . The relation is called the strict order associated with .
- Let be the set of real numbers, let , let be functions on the open interval , and let . Let and be the functions from to whose values at are and…