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Theorem con34bdc 803
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
StepHypRef Expression
1 con3 606 . 2  |-  ( (
ph  ->  ps )  -> 
( -.  ps  ->  -. 
ph ) )
2 condc 787 . 2  |-  (DECID  ps  ->  ( ( -.  ps  ->  -. 
ph )  ->  ( ph  ->  ps ) ) )
31, 2impbid2 141 1  |-  (DECID  ps  ->  ( ( ph  ->  ps ) 
<->  ( -.  ps  ->  -. 
ph ) ) )
Colors of variables: wff set class
Syntax hints:   -. wn 3    -> wi 4    <-> wb 103  DECID wdc 780
This theorem was proved from axioms:  ax-1 5  ax-2 6  ax-mp 7  ax-ia1 104  ax-ia2 105  ax-ia3 106  ax-in1 579  ax-in2 580  ax-io 665
This theorem depends on definitions:  df-bi 115  df-dc 781
This theorem is referenced by:  pm4.14dc  825  algcvgblem  11124
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