Theorem 1p8e9

Description: 1 + 8 = 9. (Contributed by SN, 24-Aug-2026)

	Ref	Expression
Assertion	1p8e9	$$⊢1+8=9$$

Proof

Step	Hyp	Ref	Expression
1		df-8	$$⊢8=7+1$$
2	1	oveq2i	$$⊢1+8=1+7+1$$
3		ax-1cn	$$⊢1\in ℂ$$
4		7cn	$$⊢7\in ℂ$$
5	3 4 3	addassi	$$⊢1+7+1=1+7+1$$
6		1p7e8	$$⊢1+7=8$$
7	6	oveq1i	$$⊢1+7+1=8+1$$
8		8p1e9	$$⊢8+1=9$$
9	7 8	eqtri	$$⊢1+7+1=9$$
10	2 5 9	3eqtr2i	$$⊢1+8=9$$