Theorem necon2d 2264

Description: Contrapositive inference for inequality. (Contributed by NM, 28-Dec-2008.)

Hypothesis

Ref	Expression
necon2d.1	|- ( ph -> ( A = B -> C =/= D ) )

Assertion

Ref	Expression
necon2d	|- ( ph -> ( C = D -> A =/= B ) )

Proof of Theorem necon2d

Step	Hyp	Ref	Expression
1		necon2d.1	. . 3 |- ( ph -> ( A = B -> C =/= D ) )
2		df-ne 2206	. . 3 |- ( C =/= D <-> -. C = D )
3	1, 2	syl6ib 150	. 2 |- ( ph -> ( A = B -> -. C = D ) )
4	3	necon2ad 2262	1 |- ( ph -> ( C = D -> A =/= B ) )

Syntax hints:   -. wn 3   -> wi 4   = wceq 1243   =/= wne 2204

This theorem was proved from axioms:  ax-1 5  ax-2 6  ax-mp 7  ax-ia1 99  ax-ia2 100  ax-ia3 101  ax-in1 544  ax-in2 545

This theorem depends on definitions:  df-bi 110  df-ne 2206

This theorem is referenced by: (None)