Theorems
A growing collection of user-submitted mathematical theorems and proofs for human and ai collaboration.
Addition of Exponents for Natural Number Powers in a Field
lemmalem:natural-power-exponent-addition-2026aAlgebraLet be a field, let , and let be the set of natural numbers, with addition as in that definition. Powers are those of Natural Number Power of an Element of a Field. ThenArithmetic, Order, Discreteness and Intervals of the Integers
lemmalem:integers-arithmetic-order-2026bAnalysisAlgebraThe integers split into zero, the positive and the negative naturals, are closed under the ring operations, have no element strictly between 0 and 1, and the integers from a to b form a finite set with b-a+1 elements.The Rational Numbers as a Subset of the Real Numbers
definitiondef:rational-numbers-2026aAnalysisAlgebraLet be the real numbers, a field in which denotes the multiplicative inverse of a nonzero element , and let be the set of integers. The set of rational numbers is…- Let be the real numbers, an ordered field whose additive identity is and in which denotes the additive inverse of , let be the set of natural numbers, and let be the canonical map of . The set of…
The Determinant of a Triangular Matrix is the Product of its Diagonal Entries
lemmalem:determinant-triangular-2026aAlgebraLinear AlgebraLet be a natural number, let be the initial segment determined by , ordered by the relations of Order on the Natural Numbers, and let be a real matrix. Call lower triangular if whenever and , and upper triangular if…- Let be a natural number, let be the initial segment determined by , and let and be real matrices. Let be the matrix product, and let determinants be read as in Row Properties of the Determinant. Then
- Let be a natural number, let be the initial segment determined by , and let be the set of real numbers with the operations and the order of its ordered field structure. Let be a real matrix, with entry notation as there. Let …
- Let be a natural number, let be the initial segment determined by , and let be the set of permutations of , with the identity , the composition and the inverse of…
Permutations of an Initial Segment Form a Group under Composition
lemmalem:permutation-group-2026aAlgebraCombinatoricsLet be a natural number, let be the initial segment determined by , that is, the set , and let be the set of permutations of , that is, the set of bijections from to . For maps let be th…Generalized Distributivity: Expanding a Product of Finite Sums
lemmalem:generalized-distributivity-2026aAlgebraSet TheoryLet be a field. Let be the set of natural numbers with successor map as in that definition, let , and let and be the initial segments they determine. Let be an -tuple of -tuples in , with components written …The Product of Two Sums over Finite Index Sets is a Sum over the Cartesian Product
lemmalem:finite-set-indexed-sum-product-2026aAlgebraSet TheoryLet be a field, let and be nonempty finite sets, and let and be maps. Let be the Cartesian product of and , formed with the ordered pair; it is nonempty, and it is finite by claim 1 of…Peeling, Splitting, and Interchange for Sums over a Finite Index Set
lemmalem:finite-set-indexed-sum-peeling-2026aAlgebraSet TheoryLet be a field, with additive identity . Let be the set of natural numbers with successor map as in that definition. The notions finite and has elements are those of the indicated definitions. Sums over a finite index set are those of…Properties of Natural Number Powers in a Field
lemmalem:natural-power-properties-2026bAnalysisAlgebraNatural powers in a field satisfy the recursion and the unit and product rules, vanish only at 0, and add exponents; for real bases they are monotone in a nonnegative base and, for bases at least 1, in the exponent.- Let be a field, let , let be a natural number, and let be the initial segment determined by . The th power of is the finite product of the map whose value at every is .
Properties of a Sum over a Finite Index Set
lemmalem:finite-set-indexed-sum-properties-2026aAlgebraSet TheoryLet be a field, let and be nonempty finite sets, let and be maps, and let . Sums over a finite index set are those of Sum over a Finite Index Set, and sums with a numerical index range are the finite sums of . Then the following…- Let be a field, let be a nonempty finite set, let be the natural number for which has elements, unique by Uniqueness of the Number of Elements, let be the initial segment determined by , and let be a map. The sum of over is…
A Sum over a Finite Index Set Does Not Depend on the Enumeration
lemmalem:finite-set-indexed-sum-well-defined-2026aAlgebraSet TheoryLet be a field, let be a nonempty finite set, and let be a natural number such that has elements; such an is unique by Uniqueness of the Number of Elements. Let be the initial segment determined by , and let be a map. Sums below are the…Invariance of Finite Sums and Products under Reindexing by a Permutation
lemmalem:finite-sum-product-permutation-invariance-2026aAlgebraSet TheoryLet be a field. Let be the set of natural numbers, let , and let be the initial segment determined by . Let be a map with values written , and let be a bijection. Sums and products below are the…Extraction of a Term from a Finite Sum or Product in a Field
lemmalem:finite-sum-product-extraction-2026aAlgebraSet TheoryLet be a field. Let be the set of natural numbers with successor map as in that definition, ordered by the relations of Order on the Natural Numbers, and for let be the initial segment determined by . Let , let…- Let be a field, with additive identity and multiplicative identity . Let be the set of natural numbers with successor map as in that definition, ordered by the relations of Order on the Natural Numbers, let , and let be the…