Theorem preq2i

Description: Equality inference for unordered pairs. (Contributed by NM, 19-Oct-2012)

	Ref	Expression
Hypothesis	preq1i.1	|- A = B
Assertion	preq2i	|- { C , A } = { C , B }

Proof

Step	Hyp	Ref	Expression
1		preq1i.1	|- A = B
2		preq2	|- ( A = B -> { C , A } = { C , B } )
3	1 2	ax-mp	|- { C , A } = { C , B }