Theorem 2p7e9

Description: 2 + 7 = 9. (Contributed by SN, 24-Aug-2026)

	Ref	Expression
Assertion	2p7e9	|- ( 2 + 7 ) = 9

Proof

Step	Hyp	Ref	Expression
1		2cn	|- 2 e. CC
2		5cn	|- 5 e. CC
3	1 2 1	addassi	|- ( ( 2 + 5 ) + 2 ) = ( 2 + ( 5 + 2 ) )
4		2p5e7	|- ( 2 + 5 ) = 7
5	4	oveq1i	|- ( ( 2 + 5 ) + 2 ) = ( 7 + 2 )
6		7p2e9	|- ( 7 + 2 ) = 9
7	5 6	eqtri	|- ( ( 2 + 5 ) + 2 ) = 9
8		5p2e7	|- ( 5 + 2 ) = 7
9	8	oveq2i	|- ( 2 + ( 5 + 2 ) ) = ( 2 + 7 )
10	3 7 9	3eqtr3ri	|- ( 2 + 7 ) = 9