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Theorem pm4.66 409
Description: Theorem *4.66 of [WhiteheadRussell] p. 120. (Contributed by NM, 3-Jan-2005.)
Assertion
Ref Expression
pm4.66  |-  ( ( -.  ph  ->  -.  ps ) 
<->  ( ph  \/  -.  ps ) )

Proof of Theorem pm4.66
StepHypRef Expression
1 pm4.64 361 1  |-  ( ( -.  ph  ->  -.  ps ) 
<->  ( ph  \/  -.  ps ) )
Colors of variables: wff set class
Syntax hints:   -. wn 3    -> wi 4    <-> wb 176    \/ wo 357
This theorem is referenced by:  pm4.54  479  hirstL-ax3  27860
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  df-or 359
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