Metamath Proof Explorer

Theorem uneq2d

Description: Deduction adding union to the left in a class equality. (Contributed by NM, 29-Mar-1998)

Ref Expression
Hypothesis uneq1d.1 φ A = B
Assertion uneq2d φ C A = C B


Step Hyp Ref Expression
1 uneq1d.1 φ A = B
2 uneq2 A = B C A = C B
3 1 2 syl φ C A = C B