Theorem necon1i 2561

Description: Contrapositive inference for inequality. (Contributed by NM, 18-Mar-2007.)

Hypothesis

Ref	Expression
necon1i.1	|- (A =/= B -> C = D)

Assertion

Ref	Expression
necon1i	|- (C =/= D -> A = B)

Proof of Theorem necon1i

Step	Hyp	Ref	Expression
1		df-ne 2519	. . 3 |- (A =/= B <-> -. A = B)
2		necon1i.1	. . 3 |- (A =/= B -> C = D)
3	1, 2	sylbir 204	. 2 |- (-. A = B -> C = D)
4	3	necon1ai 2559	1 |- (C =/= D -> A = B)

Syntax hints:  -. wn 3   -> wi 4   = wceq 1642   =/= wne 2517

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 2519

This theorem is referenced by:  map0b  6025