Theorem 1p7e8

Description: 1 + 7 = 8. (Contributed by SN, 24-Aug-2026)

	Ref	Expression
Assertion	1p7e8	$$⊢1+7=8$$

Proof

Step	Hyp	Ref	Expression
1		df-7	$$⊢7=6+1$$
2	1	oveq2i	$$⊢1+7=1+6+1$$
3		ax-1cn	$$⊢1\in ℂ$$
4		6cn	$$⊢6\in ℂ$$
5	3 4 3	addassi	$$⊢1+6+1=1+6+1$$
6		1p6e7	$$⊢1+6=7$$
7	6	oveq1i	$$⊢1+6+1=7+1$$
8		7p1e8	$$⊢7+1=8$$
9	7 8	eqtri	$$⊢1+6+1=8$$
10	2 5 9	3eqtr2i	$$⊢1+7=8$$