Metamath Proof Explorer

Theorem difeq2d

Description: Deduction adding difference to the left in a class equality. (Contributed by NM, 15-Nov-2002)

Ref Expression
Hypothesis difeq1d.1 φ A = B
Assertion difeq2d φ C A = C B


Step Hyp Ref Expression
1 difeq1d.1 φ A = B
2 difeq2 A = B C A = C B
3 1 2 syl φ C A = C B