Theorem 9p4e13

Description: 9 + 4 = 13. (Contributed by Mario Carneiro, 19-Apr-2015)

	Ref	Expression
Assertion	9p4e13	$$⊢9+4=13$$

Proof

Step	Hyp	Ref	Expression
1		9nn0	$$⊢9\in {\mathbb{N}}_0$$
2		3nn0	$$⊢3\in {\mathbb{N}}_0$$
3		2nn0	$$⊢2\in {\mathbb{N}}_0$$
4		df-4	$$⊢4=3+1$$
5		df-3	$$⊢3=2+1$$
6		9p3e12	$$⊢9+3=12$$
7	1 2 3 4 5 6	6p5lem	$$⊢9+4=13$$