Natural Numbers

🅟 Mar 19, 2026

  🅤 Apr 21, 2026

NN#DEF. Natural Numbers.

  • The set of natural numbers $\N$ is defined as the smallest inductive set [see Natural Numbers (Set Theory)].

  • The arithmetic on $\N$ is as defined for ordinals (see Ordinal Arithmetic), but without any concern for limit ordinals.

  • As defined for ordinals, the following gives a well-order on $\N$:

    \[n<m \enspace\lrimp\enspace n\in m.\]
  • The set of positive natural numbers is

    \[\N^+ = \N\setminus\{0\}.\]

NN#PROP-A.

$(\N,+,\leq)$ is a well-ordered abelian monoid with neutral element $0$.

NN#PROP-M.

$(\N^+,\cdot,\leq)$ is a well-ordered abelian monoid with neutral element $1$.