Theorem 9p6e15

Description: 9 + 6 = 15. (Contributed by Mario Carneiro, 19-Apr-2015)

	Ref	Expression
Assertion	9p6e15	⊢ ( 9 + 6 ) = ; 1 5

Proof

Step	Hyp	Ref	Expression
1		9nn0	⊢ 9 ∈ ℕ0
2		5nn0	⊢ 5 ∈ ℕ0
3		4nn0	⊢ 4 ∈ ℕ0
4		df-6	⊢ 6 = ( 5 + 1 )
5		df-5	⊢ 5 = ( 4 + 1 )
6		9p5e14	⊢ ( 9 + 5 ) = ; 1 4
7	1 2 3 4 5 6	6p5lem	⊢ ( 9 + 6 ) = ; 1 5