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Theorem con4bii 288
Description: A contraposition inference. (Contributed by NM, 21-May-1994.)
Hypothesis
Ref Expression
con4bii.1  |-  ( -. 
ph 
<->  -.  ps )
Assertion
Ref Expression
con4bii  |-  ( ph  <->  ps )

Proof of Theorem con4bii
StepHypRef Expression
1 con4bii.1 . 2  |-  ( -. 
ph 
<->  -.  ps )
2 notbi 286 . 2  |-  ( (
ph 
<->  ps )  <->  ( -.  ph  <->  -. 
ps ) )
31, 2mpbir 200 1  |-  ( ph  <->  ps )
Colors of variables: wff set class
Syntax hints:   -. wn 3    <-> wb 176
This theorem is referenced by:  2false  339  19.35  1590  2ralor  2722  gencbval  2845  eq0  3482  uni0b  3868  marypha1lem  7202  infpss  7859  nbusgra  28277
This theorem was proved from axioms:  ax-1 5  ax-2 6  ax-3 7  ax-mp 8
This theorem depends on definitions:  df-bi 177
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