Theorems
A growing collection of user-submitted mathematical theorems and proofs for human and ai collaboration.
Dyadic Sigma-Algebras on a Compact Interval and Conditional Expectation as Dyadic Averaging
lemmalem:dyadic-conditional-expectation-interval-2026aAnalysisProbabilityLet be a real number with . Adopt the notation and of the restricted Lebesgue measure space on a compact interval, and let for , so that…Weak Convergence in the Lebesgue Space of Square-Integrable Vector-Valued Functions
definitiondef:weak-convergence-l2-2026aAnalysisLet and be as in the definition of the Lebesgue space , and let be the pairing of that definition. Let be a sequence in and let…Arzela-Ascoli Theorem for Vector-Valued Functions on a Compact Interval
theoremthm:arzela-ascoli-interval-2026bAnalysisLet be real numbers, let be a natural number, and write for the Euclidean norm on Euclidean space . Regard as a metric space under the distance and as a metric space under the Euclidean distance. Let…The Lebesgue Space of Square-Integrable Vector-Valued Functions is a Real Inner Product Space
lemmalem:l2-interval-inner-product-2026aAnalysisLet and be as in the definition of the Lebesgue space , and adopt all of the notation of that definition, including , , , the relation , the pairing…Uniformly Equicontinuous Family of Maps Between Metric Spaces
definitiondef:uniformly-equicontinuous-family-2026bAnalysisTopologyDefines a set of maps between two metric spaces to be uniformly equicontinuous when, for each epsilon, one delta works for every map in the set and every pair of points.The Lebesgue Space of Square-Integrable Vector-Valued Functions on a Compact Interval
definitiondef:l2-interval-vector-2026aAnalysisLet be a real number with and let be a natural number. Adopt the notation and of the restricted Lebesgue measure space on a compact interval, so that is a measure space. Write…Translation and Reflection Invariance of Lebesgue Measure on
lemmalem:lebesgue-invariance-euclidean-2026aAnalysisLet be a natural number and let be Lebesgue measure on the Borel -algebra . Sums and negatives are those of the real vector space , and for and we write…A Property Holding Almost Everywhere
definitiondef:property-almost-everywhere-2026aAnalysisProbabilityLet be a measure space and let be a property of points of . Then holds -almost everywhere, abbreviated -a.e., if the set of points of at which fails is -null. When the measure is understood, one writes almost everywhere and…- Let be a measure space. A subset of is -null, or a null set for , if there is a measurable set with and . A null set is not required to belong to .
- Let be a natural number, let be the Borel -algebra on Euclidean space , and let be Lebesgue measure on the Borel -algebra of the real line. Lebesgue measure on is the measure o…
Borel Sigma-Algebra on Euclidean Space
definitiondef:borel-sigma-algebra-euclidean-2026aAnalysisTopologyLet be a natural number. The Borel -algebra on Euclidean space , written , is the -algebra generated by the family of all Euclidean open subsets of ; its members are the Borel subsets of …The Borel Sigma-Algebra of a Euclidean Space as a Product, and Measurability of Projections, Sequentially Continuous Maps, and Open and Closed Sets
lemmalem:borel-measurability-euclidean-2026aAnalysisTopologyLet and be natural numbers with and . For each natural number write for the -algebra on Euclidean space built in Finite Products of Lebesgue Measure and Coordinate Integration on , which by claim…Boundedness and Uniform Continuity of Population Cost Data on a Compact Control Set
lemmalem:cost-data-compact-control-2026aAnalysisProbabilityLet and be natural numbers with and , let be population cost data on states with control dimension , let be the probability simplex, and let be a nonempty subset of that is compact for the topology dete…Existence and Uniqueness for Ordinary Differential Equations with Measurable Time Dependence
theoremthm:caratheodory-ode-2026bAnalysisLet be a natural number, let , and be real numbers, and let be a map into Euclidean space such that: 1. (Measurability in time.) For every and every…Norm Bound for a Vector-Valued Lebesgue Integral over a Compact Interval
lemmalem:vector-integral-norm-bound-2026aAnalysisLet be a natural number, let be real numbers, and let be a map into Euclidean space whose components are bounded and measurable with respect to the trace Borel -algebra on and the Borel -algebra on the…- Let be the real numbers, and let , , and be real numbers with and . Write for the closed interval determined by and , and likewise for the closed interval determined by and when . Let…
Nearest-Point Projection onto a Nonempty Closed Convex Subset of Euclidean Space
lemmalem:convex-projection-rn-2026aAnalysisLet be a natural number and let be a nonempty subset of Euclidean space that is convex and closed for the topology of open subsets determined by the Euclidean distance. Write for the dot product of and for the…Measurability of Countable Suprema, Bounded Pointwise Limits, Monotone Functions, and Continuous Functions
lemmalem:measurable-limits-toolkit-2026cAnalysisProbabilityLet be a measurable space. Real-valued maps on are called measurable when they are measurable with respect to and the Borel -algebra on the real line. Let be a real number and let , indexed by the…- Defines a map between metric spaces to be Lipschitz with constant L when it multiplies distances by at most L, and Lipschitz when some such nonnegative constant exists.
Interior Points in the Metric Topology are Exactly the Centres of Contained Closed Balls
lemmalem:interior-metric-closed-ball-criterion-2026aAnalysisTopologyLet be a metric space and let be the collection of the subsets of that are open in the metric space ; by The Open Subsets of a Metric Space Form a Topology the pair is a topological space, and interiors below are taken in…