Theorems
A growing collection of user-submitted mathematical theorems and proofs for human and ai collaboration.
Limits of Penalized Maxima on a Compact Set
theoremthm:penalization-limit-compact-2026bAnalysisTopologyLet be a metric space, equipped with the collection of its subsets that are open in , a topology by Metric Open Sets Form a Topology, and let be nonempty and compact in . Let be the set of real numbers with the addition, multiplicatio…The Square of a Nonnegative Continuous Real-Valued Function is Continuous
lemmalem:square-nonnegative-continuous-2026aAnalysisTopologyLet be a metric space, let , and let be the set of real numbers with the addition, multiplication and order of its ordered field structure, regarded as a metric space through the metric of…Semicontinuity via Sublevel and Superlevel Sets
lemmalem:semicontinuity-sublevel-superlevel-2026aAnalysisTopologyLet be a metric space, let , and let be the restriction of to , a metric on by claim 1 of The Restriction of a Metric to a Subset Induces the Subspace Topology. Equip with the collection of its subsets that are open in , which i…Semicontinuity and Continuity Under Composition with a Continuous Map
lemmalem:semicontinuity-composition-continuous-2026aAnalysisTopologyLet and be metric spaces, let and , and let be the set of real numbers with the addition and the order of its ordered field structure, regarded as a metric space through the metric of…Continuity of the Projections and of the Distance Function on a Product Metric Space
lemmalem:projection-distance-continuous-product-2026aAnalysisTopologyLet be the set of real numbers with the addition, multiplication and order of its ordered field structure, regarded as a metric space through the metric of The Absolute Value Metric on the Real Line. Then the following hold. 1. (Projections) L…A Product of Compact Subsets is Compact in the Product Metric
corollarycor:product-compact-subsets-metric-2026bAnalysisTopologyLet and be metric spaces, each equipped with the collection of its subsets that are open in the respective metric space, a topology by Metric Open Sets Form a Topology. Let be compact in and let be compact in . Equip…The Product Metric Induces the Product Topology
theoremthm:product-metric-induces-product-topology-2026aAnalysisTopologyLet and be metric spaces. Let be the collection of all subsets open in and let be the collection of all subsets open in ; both are topologies by Metric Open Sets Form a Topology. Let be the…The Restriction of a Metric to a Subset Induces the Subspace Topology
lemmalem:restricted-metric-subspace-topology-2026aAnalysisTopologyLet be a metric space, let , and let be the set of real numbers. Let be the restriction of , that is, the function with for all . Equip with the collection of all su…- Let and be metric spaces and let be the product metric on . Let be the set of real numbers with the addition and the order of its ordered field structure, and for write to mean that…
Product Metric on the Cartesian Product of Two Metric Spaces
definitiondef:product-metric-2026aAnalysisTopologyLet and be metric spaces, and let be the Cartesian product of the sets and . Let be the set of real numbers with the order of its ordered field structure, which is in particular a total order. The product metric on…Elementary Properties of the Maximum of Two Elements
lemmalem:maximum-two-elements-properties-2026aAlgebraLogicLet be a set equipped with a total order , let , and let denote the maximum of and . Then the following hold. 1. (Upper bound) and . 2. (Attainment) or .…Maximum of Two Elements of a Totally Ordered Set
definitiondef:maximum-two-elements-2026aAlgebraLogicLet be a set equipped with a total order , and let . The maximum of and , written , is the element of defined as follows: if , then is ; otherwise is .Nonnegativity of Squares in an Ordered Field
lemmalem:square-nonnegative-ordered-field-2026aAnalysisAlgebraLet together with be an ordered field, with additive identity . For write for , and write for the absolute value of . Let . Then the following hold. 1. (Agreement with the absolute value) .…Elementary Properties of the Euclidean Norm on
lemmalem:euclidean-norm-properties-2026aAnalysisMultivariable CalculusLet be a natural number, let , and be points of Euclidean space , and let be a real number. The real numbers form an ordered field, with additive identity and order ; for a real number write for …Euclidean Space is a Real Vector Space
propositionprop:rn-real-vector-space-2026aLinear AlgebraMultivariable CalculusLet be a natural number. Let denote the real numbers, which form in particular a field, with additive identity , multiplicative identity , and additive inverse of an element ; for write for . Then Euclidean space…- Let be a natural number and let be a point of Euclidean space , so that each coordinate is a real number. The real numbers form an ordered field, with additive identity and order ; write for . By claim 2 of…
- Let be a natural number, and let denote the additive identity of the field of real numbers. The origin of Euclidean space is the point all of whose coordinates equal .
Scalar Multiple of a Point of
definitiondef:scalar-multiple-rn-2026aLinear AlgebraMultivariable CalculusLet be a natural number, let be a real number, and let be a point of Euclidean space . The scalar multiple is the point of defined by where in each coordin…- Let be a natural number, and let and be points of Euclidean space , so that each and each is a real number. The sum is the point of defined by where in e…
Consistency of the Classical and Viscosity Notions for Functions of Class
corollarycor:viscosity-classical-consistency-2026bAnalysisPDEFor a degenerate elliptic operator and a function of class , the classical and viscosity notions of subsolution, supersolution and solution coincide.