Metamath Proof Explorer


Theorem psseq2i

Description: An equality inference for the proper subclass relationship. (Contributed by NM, 9-Jun-2004)

Ref Expression
Hypothesis psseq1i.1 A = B
Assertion psseq2i C A C B

Proof

Step Hyp Ref Expression
1 psseq1i.1 A = B
2 psseq2 A = B C A C B
3 1 2 ax-mp C A C B