Theorem uneq2i

Description: Inference adding union to the left in a class equality. (Contributed by NM, 30-Aug-1993)

	Ref	Expression
Hypothesis	uneq1i.1	|- A = B
Assertion	uneq2i	|- ( C u. A ) = ( C u. B )

Proof

Step	Hyp	Ref	Expression
1		uneq1i.1	|- A = B
2		uneq2	|- ( A = B -> ( C u. A ) = ( C u. B ) )
3	1 2	ax-mp	|- ( C u. A ) = ( C u. B )