Theorem con34bdc 861

Description: Contraposition. Theorem *4.1 of [WhiteheadRussell] p. 116, but for a decidable proposition. (Contributed by Jim Kingdon, 24-Apr-2018.)

Assertion

Ref	Expression
con34bdc	|- (DECID ps -> ( ( ph -> ps ) <-> ( -. ps -> -. ph ) ) )

Proof of Theorem con34bdc

Step	Hyp	Ref	Expression
1		con3 632	. 2 |- ( ( ph -> ps ) -> ( -. ps -> -. ph ) )
2		condc 843	. 2 |- (DECID ps -> ( ( -. ps -> -. ph ) -> ( ph -> ps ) ) )
3	1, 2	impbid2 142	1 |- (DECID ps -> ( ( ph -> ps ) <-> ( -. ps -> -. ph ) ) )

Syntax hints:   -. wn 3   -> wi 4   <-> wb 104  DECID wdc 824

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-ia1 105  ax-ia2 106  ax-ia3 107  ax-in1 604  ax-in2 605  ax-io 699

This theorem depends on definitions:  df-bi 116  df-stab 821  df-dc 825

This theorem is referenced by:  pm4.14dc  880  algcvgblem  11981