Metamath Proof Explorer


Theorem psseq1i

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

Ref Expression
Hypothesis psseq1i.1 A=B
Assertion psseq1i ACBC

Proof

Step Hyp Ref Expression
1 psseq1i.1 A=B
2 psseq1 A=BACBC
3 1 2 ax-mp ACBC