Theorem nelneq2 2239

Description: A way of showing two classes are not equal. (Contributed by NM, 12-Jan-2002.)

Assertion

Ref	Expression
nelneq2	|- ( ( A e. B /\ -. A e. C ) -> -. B = C )

Proof of Theorem nelneq2

Step	Hyp	Ref	Expression
1		eleq2 2201	. . 3 |- ( B = C -> ( A e. B <-> A e. C ) )
2	1	biimpcd 158	. 2 |- ( A e. B -> ( B = C -> A e. C ) )
3	2	con3dimp 624	1 |- ( ( A e. B /\ -. A e. C ) -> -. B = C )

Syntax hints:   -. wn 3   -> wi 4   /\ wa 103   = wceq 1331   e. wcel 1480

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-ia1 105  ax-ia2 106  ax-ia3 107  ax-in1 603  ax-in2 604  ax-5 1423  ax-gen 1425  ax-ie1 1469  ax-ie2 1470  ax-4 1487  ax-17 1506  ax-ial 1514  ax-ext 2119

This theorem depends on definitions:  df-bi 116  df-cleq 2130  df-clel 2133

This theorem is referenced by:  dtruarb  4110  fzneuz  9874