Theorem 9p8e17

Description: 9 + 8 = 17. (Contributed by Mario Carneiro, 19-Apr-2015)

	Ref	Expression
Assertion	9p8e17	⊢ ( 9 + 8 ) = ; 1 7

Proof

Step	Hyp	Ref	Expression
1		9nn0	⊢ 9 ∈ ℕ0
2		7nn0	⊢ 7 ∈ ℕ0
3		6nn0	⊢ 6 ∈ ℕ0
4		df-8	⊢ 8 = ( 7 + 1 )
5		df-7	⊢ 7 = ( 6 + 1 )
6		9p7e16	⊢ ( 9 + 7 ) = ; 1 6
7	1 2 3 4 5 6	6p5lem	⊢ ( 9 + 8 ) = ; 1 7