Theorem 9p6e15

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

	Ref	Expression
Assertion	9p6e15	$$⊢9+6=15$$

Proof

Step	Hyp	Ref	Expression
1		9nn0	$$⊢9\in {\mathbb{N}}_0$$
2		5nn0	$$⊢5\in {\mathbb{N}}_0$$
3		4nn0	$$⊢4\in {\mathbb{N}}_0$$
4		df-6	$$⊢6=5+1$$
5		df-5	$$⊢5=4+1$$
6		9p5e14	$$⊢9+5=14$$
7	1 2 3 4 5 6	6p5lem	$$⊢9+6=15$$