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 e. NN0
2		5nn0	|- 5 e. NN0
3		4nn0	|- 4 e. NN0
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