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Theorem pm4.57 499
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 498 . 2  |-  ( (
ph  \/  ps )  <->  -.  ( -.  ph  /\  -.  ps ) )
21bicomi 205 1  |-  ( -.  ( -.  ph  /\  -.  ps )  <->  ( ph  \/  ps ) )
Colors of variables: wff setvar class
Syntax hints:   -. wn 3    <-> wb 187    \/ wo 369    /\ wa 370
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 188  df-or 371  df-an 372
This theorem is referenced by:  nanbiOLDOLD  1390  gcdaddmlem  14470  arg-ax  31062  tsbi2  32284
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