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 ∈ ℂ
4		6cn	⊢ 6 ∈ 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