Theorem necon3bid 2551

Description: Deduction from equality to inequality. (Contributed by NM, 23-Feb-2005.) (Proof shortened by Andrew Salmon, 25-May-2011.)

Hypothesis

Ref	Expression
necon3bid.1	|- (ph -> (A = B <-> C = D))

Assertion

Ref	Expression
necon3bid	|- (ph -> (A =/= B <-> C =/= D))

Proof of Theorem necon3bid

Step	Hyp	Ref	Expression
1		df-ne 2518	. 2 |- (A =/= B <-> -. A = B)
2		necon3bid.1	. . 3 |- (ph -> (A = B <-> C = D))
3	2	necon3bbid 2550	. 2 |- (ph -> (-. A = B <-> C =/= D))
4	1, 3	syl5bb 248	1 |- (ph -> (A =/= B <-> C =/= D))

Syntax hints:  -. wn 3   -> wi 4   <-> wb 176   = wceq 1642   =/= wne 2516

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8

This theorem depends on definitions:  df-bi 177  df-ne 2518

This theorem is referenced by:  nebi  2587  nchoicelem17  6305