Definition:Natural Numbers/Elements of Minimal Infinite Successor Set

Definition

The natural numbers can be defined as the elements of $\omega$.

Following Definition 2 of $\omega$, this amounts to defining the natural numbers as the finite ordinals.

In terms of the empty set $\varnothing$ and successor sets, we thus define:

$0 := \varnothing = \left\{{}\right\}$

$1 := 0^+ = 0 \cup \left\{{0}\right\} = \left\{{0}\right\}$

$2 := 1^+ = 1 \cup \left\{{1}\right\} = \left\{{0, 1}\right\}$

$3 := 2^+ = 2 \cup \left\{{2}\right\} = \left\{{0, 1, 2}\right\}$

$\vdots$

This can be expressed in detail as:

$0 := \varnothing$

$1 := \left\{{\varnothing}\right\}$

$2 := \left\{{\varnothing, \left\{{\varnothing}\right\}}\right\}$

$3 := \left\{{\varnothing, \left\{{\varnothing}\right\}, \left\{{\varnothing, \left\{{\varnothing}\right\}}\right\}}\right\}$

$\vdots$