Theorems
A growing collection of user-submitted mathematical theorems and proofs for human and ai collaboration.
- Let be a field, let be the set of natural numbers, ordered by the relations of Order on the Natural Numbers, and for let be the initial segment determined by , that is, the set of with . Sums below are the…
Semiconvex Function on a Convex Subset of
definitiondef:semiconvex-function-rn-2026aAnalysisPDEMultivariable CalculusLet be a natural number, let be the real numbers, let be convex, let , and let satisfy . Write for the Euclidean norm on . We say that is…Convex Real-Valued Function on a Convex Subset of
definitiondef:convex-function-rn-2026aAnalysisMultivariable CalculusLet be a natural number, let be the real numbers, let be convex, and let . We say that is convex on if for all and every with and ,…- Let be a natural number, let be the ordered field of real numbers, and regard Euclidean space as a real vector space by Euclidean Space is a Real Vector Space, with the sum of points and the scalar multiple . A…
Comparison Principle for First-Order Strictly Proper Equations by Doubling of Variables
theoremthm:comparison-first-order-strictly-proper-2026bAnalysisPDEDoubling of variables yields comparison on a bounded domain for a strictly proper operator that does not depend on the matrix argument and satisfies a structure condition with a modulus of continuity.Comparison of a Viscosity Subsolution with a Strict Classical Supersolution
theoremthm:comparison-c2-strict-supersolution-2026bAnalysisPDEOn a bounded domain, a viscosity subsolution of a proper operator lies below any lower semicontinuous strict classical supersolution that dominates it on the boundary.Viscosity Subsolution and Supersolution up to the Boundary
definitiondef:viscosity-sub-supersolution-boundary-2026bAnalysisPDEA function on the closure of an open set is a viscosity sub- or supersolution up to the boundary when it is semicontinuous on the closure and its restriction to the open set is a viscosity sub- or supersolution there.A Strictly Proper Second-Order Equation Operator is Proper
propositionprop:strictly-proper-implies-proper-2026aAnalysisPDELet be a natural number, let be an open subset of Euclidean space , let be the ordered field of real numbers, and let be a second-order equation operator on . If there exists with …Strictly Proper Second-Order Equation Operator
definitiondef:strictly-proper-operator-2026aAnalysisPDELet be a natural number, let be an open subset of Euclidean space , let be the ordered field of real numbers, let be the set of symmetric real matrices, let be a…- Defines a modulus of continuity as a nonnegative real function on the nonnegative reals whose values become arbitrarily small near zero.
A Scaled Squared Distance to a Point is of Class , with Gradient and Hessian
lemmalem:scaled-squared-distance-c2-2026bAnalysisMultivariable CalculusLet be a natural number, let be an open subset of Euclidean space , let , and let be an element of the real numbers. Write for the Euclidean distance, for the…Compactness of Intersections with Closed Sets and of Level Sets of Semicontinuous Functions
lemmalem:compact-closed-intersection-level-sets-2026aAnalysisTopologyLet be a metric space, equipped with the topology of its metric-open subsets, a topology by The Open Subsets of a Metric Space Form a Topology. Let be the ordered field of real numbers and let be compact in . Then the followi…Negation, Restriction, and Separated Differences of Semicontinuous Functions
lemmalem:semicontinuity-negation-difference-2026aAnalysisTopologyLet and be metric spaces, let and , and let be the ordered field of real numbers. Let , let be the function whose value at is , and let be t…Continuity of the Absolute Value, Maximum and Minimum of Real-Valued Functions on a Metric Space
lemmalem:absolute-value-max-min-continuous-real-metric-2026aAnalysisTopologyLet be a metric space, let , and let . Let denote the real numbers, with the addition, identities, additive inverses and order of their ordered field structure, the order being in particular a total order; for wr…Continuity of the Reciprocal of a Nonvanishing Real-Valued Function on a Metric Space
lemmalem:reciprocal-continuous-real-metric-2026aAnalysisTopologyLet be a metric space, let , and let . Let denote the real numbers, with the addition, multiplication, identities, additive inverses, multiplicative inverses and order of their ordered field structure; for write …Continuity of Sums and Products of Real-Valued Functions on a Metric Space
theoremthm:sum-product-continuous-real-metric-2026cAnalysisTopologyConstant maps are continuous, and sums, products and constant multiples of real-valued maps on a metric space that are continuous at a point, or everywhere, are again continuous there.Heine-Cantor Theorem: Continuity on a Compact Subset Implies Uniform Continuity
theoremthm:heine-cantor-compact-metric-2026aAnalysisTopologyLet and be metric spaces, and let be the collection of all subsets of that are open in , which is a topology on by The Open Subsets of a Metric Space Form a Topology. Let be compact in …Continuity of a Map Between Metric Spaces via Preimages of Open Sets
theoremthm:continuity-preimage-open-metric-2026bAnalysisTopologyA map between metric spaces is continuous if and only if the preimage of every open subset is open.Vanishing of the Distance to a Set Characterizes the Closure
lemmalem:distance-to-set-zero-closure-2026aAnalysisTopologyLet be a metric space, and let be the collection of all subsets of that are open in , which is a topology on by The Open Subsets of a Metric Space Form a Topology. Let be nonempty and let , and write…- Let be a metric space and let be nonempty, and write for the distance from a point to in . Let denote the real numbers, with the order, addition and additive inverses of their ordered field struc…