Theorem 3p1e4

Description: 3 + 1 = 4. (Contributed by Mario Carneiro, 18-Apr-2015)

	Ref	Expression
Assertion	3p1e4	$$⊢3+1=4$$

Proof

Step	Hyp	Ref	Expression
1		df-4	$$⊢4=3+1$$
2	1	eqcomi	$$⊢3+1=4$$