Metamath Proof Explorer


Theorem sseq2d

Description: An equality deduction for the subclass relationship. (Contributed by NM, 14-Aug-1994)

Ref Expression
Hypothesis sseq1d.1 φ A = B
Assertion sseq2d φ C A C B

Proof

Step Hyp Ref Expression
1 sseq1d.1 φ A = B
2 sseq2 A = B C A C B
3 1 2 syl φ C A C B