Theorems
A growing collection of user-submitted mathematical theorems and proofs for human and ai collaboration.
A Finite Sum of Vectors with Vanishing Tail
lemmalem:finite-sum-vanishing-tail-2026aAlgebraLinear AlgebraLet be a field, let be a vector space over with zero vector , let be a natural number, let be the initial segment it determines, and let be the strict order on . Let be an -tuple in and let be such that…Any Two Orthonormal Bases of a Complex Inner Product Space Have the Same Size
theoremthm:orthonormal-basis-size-invariance-2026aAnalysisLinear AlgebraLet together with be a complex inner product space, let and be natural numbers, and let and be tuples in that are both orthonormal bases of . Then .- Let be a field, let be natural numbers, and let and be the initial segments they determine. Let be an -tuple of -tuples in , with components for and , and let and be given…
The Sum of Ones is Strictly Increasing in
lemmalem:sum-of-ones-strictly-increasing-2026aAnalysisAlgebraLet be the set of natural numbers, with successor map and order relations and , and for let be the initial segment it determines. Let be the ordered field of real numbers, with additive identity and multiplicative…- Let be a set, let be a natural number, and let be the initial segment determined by , that is, the set of natural numbers with . The set is the set of all maps from to . An element is called an -tuple in ; for…
Dropping a Redundant Vector from a Spanning Family
lemmalem:span-drop-redundant-vector-2026bAlgebraLinear AlgebraLet be a field, let be a vector space over , and let be a natural number. Inequalities between natural numbers use the order relations on . Let be a tuple in that spans , let be a natural number with , and let b…Extraction of a Summand from a Finite Sum of Vectors
lemmalem:finite-sum-extraction-2026aAlgebraLinear AlgebraLet be a field, let be a vector space over , and let be a natural number. Inequalities between natural numbers use the order relations on . Let be a tuple in , with components for , and let be a natural number wi…Cauchy-Schwarz Inequality for a Positive Semi-Definite Self-Adjoint Operator
lemmalem:positive-semidefinite-cauchy-schwarz-2026bAnalysisLinear AlgebraLet together with be a complex inner product space with zero vector , and let be a linear operator on that is self-adjoint and positive semi-definite. Let denote the modulus of a complex number . Then the following hold.…A Linear Subspace is a Vector Space and Inherits an Inner Product
lemmalem:subspace-inner-product-space-2026bAnalysisAlgebraLinear AlgebraLet be a field, let be a vector space over with zero vector , and let be a linear subspace of . Then the following hold. 1. (Vector space) The set , equipped with the restrictions to of the addition and the scalar multiplication of , is a vect…The Span of a Finite Family is the Smallest Subspace Containing It
lemmalem:span-is-subspace-2026bAlgebraLinear AlgebraLet be a field, let be a vector space over , let be a natural number, let be the initial segment determined by , let be an -tuple in with components , and let be its span. Then the following hold.…Finite-Dimensional Vector Space
definitiondef:finite-dimensional-vector-space-2026bAlgebraLinear AlgebraLet be a field and let be a vector space over with zero vector . The space is finite-dimensional if , or if there exist a natural number and an -tuple that is a basis of .- Let be a field, let be a vector space over , let be a natural number, and let be an -tuple in , with components . The span of is the set…
Coordinate Isometry Determined by a Finite Orthonormal Basis
lemmalem:coordinate-isometry-orthonormal-basis-2026cAnalysisLinear AlgebraLet together with be a complex inner product space with zero vector and induced norm , and let be the map with , which is a metric on by claim 3 of…Extreme Value Theorem on a Compact Subset of a Metric Space
theoremthm:extreme-value-compact-metric-2026bAnalysisTopologyLet be a metric space, equipped with the collection of all subsets that are open in , which is a topology by Metric Open Sets Form a Topology. Let be nonempty and compact in . Let be the set of real numbers with the order of its…A Distance-Preserving Bijection is a Homeomorphism
lemmalem:distance-preserving-bijection-homeomorphism-2026bAnalysisTopologyLet and be metric spaces. Equip with the collection of all subsets that are open in , which is a topology by Metric Open Sets Form a Topology, and equip with the corresponding collection . Write…Restriction of a Continuous Map, and Continuous Images of Compact Subsets
lemmalem:continuous-restriction-compact-image-2026bTopologyLet and be topological spaces, let be a continuous map, and let be equipped with the subspace topology . Let denote the map with for every , and write…- Let be a field. Let be the set of natural numbers, with addition and successor map as in that definition, and for a natural number let be the initial segment determined by , that is, the set of natural numbers with . Let…
Greatest Element of a Finite Family in a Totally Ordered Set
lemmalem:finite-family-greatest-element-2026bSet TheoryLet be a set equipped with a total order , let be a natural number, let be the initial segment determined by , and let be an -tuple in , with components . Then there exists such that for every .Self-Adjointness, Unitarity and Orthogonal Projections Through the Adjoint in Finite Dimensions
lemmalem:operator-classes-via-adjoint-2026dAnalysisLinear AlgebraLet together with be a complex inner product space that has an orthonormal basis for some natural number , where is the set of -tuples in . By Uniqueness of the Adjoint, and Existence in Finite Dimensions every…Every Linear Operator on a Space with a Finite Orthonormal Basis is Bounded
lemmalem:finite-orthonormal-basis-operator-bounded-2026bAnalysisLinear AlgebraLet together with be a complex inner product space with induced norm , which is a norm on by claim 2 of The Induced Norm is a Norm, and Induces a Metric. Let be a natural number, let be an -tuple in th…