Theorem 1p3e4

Description: 1 + 3 = 4. (Contributed by SN, 19-Nov-2025)

	Ref	Expression
Assertion	1p3e4	$$⊢1+3=4$$

Proof

Step	Hyp	Ref	Expression
1		df-3	$$⊢3=2+1$$
2	1	oveq2i	$$⊢1+3=1+2+1$$
3		ax-1cn	$$⊢1\in ℂ$$
4		2cn	$$⊢2\in ℂ$$
5	3 4 3	addassi	$$⊢1+2+1=1+2+1$$
6		1p2e3	$$⊢1+2=3$$
7	6	oveq1i	$$⊢1+2+1=3+1$$
8		3p1e4	$$⊢3+1=4$$
9	7 8	eqtri	$$⊢1+2+1=4$$
10	2 5 9	3eqtr2i	$$⊢1+3=4$$