Theorem 9p3e12

Description: 9 + 3 = 12. (Contributed by Mario Carneiro, 19-Apr-2015)

	Ref	Expression
Assertion	9p3e12	$$⊢9+3=12$$

Proof

Step	Hyp	Ref	Expression
1		9nn0	$$⊢9\in {\mathbb{N}}_0$$
2		2nn0	$$⊢2\in {\mathbb{N}}_0$$
3		1nn0	$$⊢1\in {\mathbb{N}}_0$$
4		df-3	$$⊢3=2+1$$
5		df-2	$$⊢2=1+1$$
6		9p2e11	$$⊢9+2=11$$
7	1 2 3 4 5 6	6p5lem	$$⊢9+3=12$$