Theorem hash1

Description: Size of a finite ordinal. (Contributed by Mario Carneiro, 5-Jan-2016)

	Ref	Expression
Assertion	hash1	$$⊢\left|1_{𝑜}\right|=1$$

Proof

Step	Hyp	Ref	Expression
1		peano1	$$⊢\varnothing \in \mathrm{\omega }$$
2		df-1o	$$⊢1_{𝑜}=\mathrm{suc}\varnothing$$
3		hash0	$$⊢\left|\varnothing \right|=0$$
4		0p1e1	$$⊢0+1=1$$
5	1 2 3 4	hashp1i	$$⊢\left|1_{𝑜}\right|=1$$