Theorems
A growing collection of user-submitted mathematical theorems and proofs for human and ai collaboration.
The Natural Numbers Are Well Ordered
theoremthm:well-ordering-natural-numbers-2026aNumber TheorySet TheoryLet denote the natural numbers with the order , and let be nonempty. Then has a least element: there exists such that for every . This element is unique, and is denoted .- Let , where is the set of natural numbers with multiplication as in that definition. We say that divides , written if there exists with .
Properties of the Order on the Natural Numbers
lemmalem:order-natural-numbers-2026aNumber TheorySet TheoryLet be the set of natural numbers, with addition and successor map as in that definition, and let and be the order relations of that definition. Then the following hold for all . 1. ; if then ; ifβ¦- Let be the set of natural numbers, with addition as in that definition, and let . We write if there exists with , and we write if or . We also write for , and forβ¦
Arithmetic of Addition on the Natural Numbers
lemmalem:natural-number-addition-2026aNumber TheorySet TheoryLet be the set of natural numbers, with addition and successor map as in that definition. Then the following hold for all . 1. and . 2. . 3. (Associativity) . 4. (Commutativity)β¦Basic Properties of Initial Segments of the Natural Numbers
lemmalem:initial-segment-basic-2026aNumber TheorySet TheoryLet be the set of natural numbers with successor map , let be the order on , and let denote the initial segment determined by . Then the following hold for all . 1. and ; in particular is nonβ¦Uniqueness of the Number of Elements
lemmalem:finite-cardinality-well-defined-2026aNumber TheorySet TheoryLet be a set and let , where is the set of natural numbers and , denote the initial segments determined by and . If there exist bijections then .Initial Segment of the Natural Numbers
definitiondef:initial-segment-natural-numbers-2026aNumber TheorySet TheoryLet be the set of natural numbers and let be the order on . For , the initial segment determined by is the set also written .