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 e. CC
4		6cn	|- 6 e. CC
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