Theorem necon1ddc 2358

Description: Contrapositive law deduction for inequality. (Contributed by Jim Kingdon, 19-May-2018.)

Hypothesis

Ref	Expression
necon1ddc.1	|- ( ph -> (DECID A = B -> ( A =/= B -> C = D ) ) )

Assertion

Ref	Expression
necon1ddc	|- ( ph -> (DECID A = B -> ( C =/= D -> A = B ) ) )

Proof of Theorem necon1ddc

Step	Hyp	Ref	Expression
1		df-ne 2281	. 2 |- ( C =/= D <-> -. C = D )
2		necon1ddc.1	. . 3 |- ( ph -> (DECID A = B -> ( A =/= B -> C = D ) ) )
3	2	necon1bddc 2357	. 2 |- ( ph -> (DECID A = B -> ( -. C = D -> A = B ) ) )
4	1, 3	syl7bi 164	1 |- ( ph -> (DECID A = B -> ( C =/= D -> A = B ) ) )

Syntax hints:   -. wn 3   -> wi 4  DECID wdc 802   = wceq 1312   =/= wne 2280

This theorem was proved from axioms:  ax-1 5  ax-2 6  ax-mp 7  ax-ia1 105  ax-ia2 106  ax-ia3 107  ax-in1 586  ax-in2 587  ax-io 681

This theorem depends on definitions:  df-bi 116  df-stab 799  df-dc 803  df-ne 2281

This theorem is referenced by:  xblss2ps  12387  xblss2  12388