Theorem 4p5e9

Description: 4 + 5 = 9. (Contributed by SN, 24-Aug-2026)

	Ref	Expression
Assertion	4p5e9	⊢ ( 4 + 5 ) = 9

Proof

Step	Hyp	Ref	Expression
1		df-5	⊢ 5 = ( 4 + 1 )
2	1	oveq2i	⊢ ( 4 + 5 ) = ( 4 + ( 4 + 1 ) )
3		4cn	⊢ 4 ∈ ℂ
4		ax-1cn	⊢ 1 ∈ ℂ
5	3 3 4	addassi	⊢ ( ( 4 + 4 ) + 1 ) = ( 4 + ( 4 + 1 ) )
6		4p4e8	⊢ ( 4 + 4 ) = 8
7	6	oveq1i	⊢ ( ( 4 + 4 ) + 1 ) = ( 8 + 1 )
8		8p1e9	⊢ ( 8 + 1 ) = 9
9	7 8	eqtri	⊢ ( ( 4 + 4 ) + 1 ) = 9
10	2 5 9	3eqtr2i	⊢ ( 4 + 5 ) = 9