Theorem hash4

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

	Ref	Expression
Assertion	hash4	⊢ ( ♯ ‘ 4o ) = 4

Proof

Step	Hyp	Ref	Expression
1		3onn	⊢ 3o ∈ ω
2		df-4o	⊢ 4o = suc 3o
3		hash3	⊢ ( ♯ ‘ 3o ) = 3
4		3p1e4	⊢ ( 3 + 1 ) = 4
5	1 2 3 4	hashp1i	⊢ ( ♯ ‘ 4o ) = 4