Theorem necon3bi 2397

Description: Contrapositive inference for inequality. (Contributed by NM, 1-Jun-2007.) (Proof rewritten by Jim Kingdon, 15-May-2018.)

Hypothesis

Ref	Expression
necon3bi.1	|- ( A = B -> ph )

Assertion

Ref	Expression
necon3bi	|- ( -. ph -> A =/= B )

Proof of Theorem necon3bi

Step	Hyp	Ref	Expression
1		necon3bi.1	. . 3 |- ( A = B -> ph )
2	1	con3i 632	. 2 |- ( -. ph -> -. A = B )
3		df-ne 2348	. 2 |- ( A =/= B <-> -. A = B )
4	2, 3	sylibr 134	1 |- ( -. ph -> A =/= B )

Syntax hints:   -. wn 3   -> wi 4   = wceq 1353   =/= wne 2347

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-ia1 106  ax-ia2 107  ax-ia3 108  ax-in1 614  ax-in2 615

This theorem depends on definitions:  df-bi 117  df-ne 2348

This theorem is referenced by:  pwne  4157  sucpw1ne3  7224  nltpnft  9788  ngtmnft  9791