Theorem 1p6e7

Description: 1 + 6 = 7. (Contributed by SN, 24-Aug-2026)

	Ref	Expression
Assertion	1p6e7	⊢ ( 1 + 6 ) = 7

Proof

Step	Hyp	Ref	Expression
1		df-6	⊢ 6 = ( 5 + 1 )
2	1	oveq2i	⊢ ( 1 + 6 ) = ( 1 + ( 5 + 1 ) )
3		ax-1cn	⊢ 1 ∈ ℂ
4		5cn	⊢ 5 ∈ ℂ
5	3 4 3	addassi	⊢ ( ( 1 + 5 ) + 1 ) = ( 1 + ( 5 + 1 ) )
6		1p5e6	⊢ ( 1 + 5 ) = 6
7	6	oveq1i	⊢ ( ( 1 + 5 ) + 1 ) = ( 6 + 1 )
8		6p1e7	⊢ ( 6 + 1 ) = 7
9	7 8	eqtri	⊢ ( ( 1 + 5 ) + 1 ) = 7
10	2 5 9	3eqtr2i	⊢ ( 1 + 6 ) = 7