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Theorem pm3.1 500
Description: Theorem *3.1 of [WhiteheadRussell] p. 111. (Contributed by NM, 3-Jan-2005.)
Assertion
Ref Expression
pm3.1  |-  ( (
ph  /\  ps )  ->  -.  ( -.  ph  \/  -.  ps ) )

Proof of Theorem pm3.1
StepHypRef Expression
1 anor 491 . 2  |-  ( (
ph  /\  ps )  <->  -.  ( -.  ph  \/  -.  ps ) )
21biimpi 197 1  |-  ( (
ph  /\  ps )  ->  -.  ( -.  ph  \/  -.  ps ) )
Colors of variables: wff setvar class
Syntax hints:   -. wn 3    -> wi 4    \/ 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:  pm3.14  504
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