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Theorem pm4.57 497
Description: Theorem *4.57 of [WhiteheadRussell] p. 120. (Contributed by NM, 3-Jan-2005.)
Assertion
Ref Expression
pm4.57  |-  ( -.  ( -.  ph  /\  -.  ps )  <->  ( ph  \/  ps ) )

Proof of Theorem pm4.57
StepHypRef Expression
1 oran 496 . 2  |-  ( (
ph  \/  ps )  <->  -.  ( -.  ph  /\  -.  ps ) )
21bicomi 202 1  |-  ( -.  ( -.  ph  /\  -.  ps )  <->  ( ph  \/  ps ) )
Colors of variables: wff setvar class
Syntax hints:   -. wn 3    <-> wb 184    \/ wo 368    /\ wa 369
This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8
This theorem depends on definitions:  df-bi 185  df-or 370  df-an 371
This theorem is referenced by:  nanbi  1345  gcdaddmlem  14016  arg-ax  29446  tsbi2  30134
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