Theorem 1p3e4

Description: 1 + 3 = 4. (Contributed by SN, 19-Nov-2025)

	Ref	Expression
Assertion	1p3e4	|- ( 1 + 3 ) = 4

Proof

Step	Hyp	Ref	Expression
1		df-3	|- 3 = ( 2 + 1 )
2	1	oveq2i	|- ( 1 + 3 ) = ( 1 + ( 2 + 1 ) )
3		ax-1cn	|- 1 e. CC
4		2cn	|- 2 e. CC
5	3 4 3	addassi	|- ( ( 1 + 2 ) + 1 ) = ( 1 + ( 2 + 1 ) )
6		1p2e3	|- ( 1 + 2 ) = 3
7	6	oveq1i	|- ( ( 1 + 2 ) + 1 ) = ( 3 + 1 )
8		3p1e4	|- ( 3 + 1 ) = 4
9	7 8	eqtri	|- ( ( 1 + 2 ) + 1 ) = 4
10	2 5 9	3eqtr2i	|- ( 1 + 3 ) = 4