Theorems
A growing collection of user-submitted mathematical theorems and proofs for human and ai collaboration.
- Let be a natural number and let be a real number. Write , whose members are called channels, and write and for the -fold Borel -algebra and product Lebesgue measure on . An…
Independent Random Elements: Product Laws and Iterated Expectations
lemmalem:independence-fubini-2026bAnalysisProbabilityTwo random vectors are independent exactly when the joint law of the pair is the product of their laws; for independent random vectors, the expectation of a function of the pair is an iterated integral against the two laws (Tonelli for nonnegative functions, Fubini for integrable…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 Map, and the Set of Measurable Maps; measurability and integrals of -valued functions are those of Nonnegative Measurable Maps and Their Lebesgue Integral; measures use the conventions of…- Let be a probability space, let be a natural number, let be a measurable space, and let be a -finite measure on it. Let and be the -fold product -algebra and product of Lebesgu…
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 and Measures with a Density: Measures, Integrals and Change of Variables
lemmalem:image-measure-density-2026bAnalysisProbabilityThe image measure of a measure under a measurable function, and the measure with a nonnegative measurable density, are measures; integrals against them are integrals of the composed function, respectively of the product with the density, for nonnegative and for integrable functio…Variational Representation and Convexity of the Matrix Inverse
lemmalem:matrix-inverse-convexity-2026aLinear AlgebraLet be a natural number. All matrices below are real matrices, combined entrywise by the matrix sum and scalar multiple; denotes the dot product on the Euclidean space , and denotes the matrix-vector product.…- 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 an Open Subset of
definitiondef:gradient-euclidean-open-set-2026cAnalysisMultivariable CalculusThe gradient of a real-valued function at a point where all its partial derivatives exist is the vector of those partial derivatives; the gradient function collects these vectors.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…
Continuous Partial Derivatives Imply Differentiability
theoremthm:c1-implies-differentiable-2026cAnalysisMultivariable CalculusA function on an open subset of R^n whose partial derivatives exist throughout and are continuous at a point is differentiable there, with derivative given by the gradient, respectively the Jacobian matrix.with the Euclidean Distance Is Isometric to the Real Line
lemmalem:euclidean-distance-real-line-2026cAnalysisTopologyTaking the single component is a distance-preserving bijection from R^1 with the Euclidean distance onto the real numbers with the distance |s-t|.