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Theorem 2false 650
Description: Two falsehoods are equivalent. (Contributed by NM, 4-Apr-2005.) (Revised by Mario Carneiro, 31-Jan-2015.)
Hypotheses
Ref Expression
2false.1  |-  -.  ph
2false.2  |-  -.  ps
Assertion
Ref Expression
2false  |-  ( ph  <->  ps )

Proof of Theorem 2false
StepHypRef Expression
1 2false.1 . . 3  |-  -.  ph
21pm2.21i 608 . 2  |-  ( ph  ->  ps )
3 2false.2 . . 3  |-  -.  ps
43pm2.21i 608 . 2  |-  ( ps 
->  ph )
52, 4impbii 124 1  |-  ( ph  <->  ps )
Colors of variables: wff set class
Syntax hints:   -. wn 3    <-> wb 103
This theorem was proved from axioms:  ax-1 5  ax-2 6  ax-mp 7  ax-ia2 105  ax-ia3 106  ax-in2 578
This theorem depends on definitions:  df-bi 115
This theorem is referenced by:  bianfi  891  bifal  1300  dfnul2  3277  dfnul3  3278  rab0  3300  iun0  3769  0iun  3770  0xp  4486  cnv0  4801  co02  4910  0er  6278  bdnth  11163  bdnthALT  11164
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