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Theorem pm2.85 826
Description: Theorem *2.85 of [WhiteheadRussell] p. 108. (Contributed by NM, 3-Jan-2005.) (Proof shortened by Wolf Lammen, 5-Jan-2013.)
Assertion
Ref Expression
pm2.85  |-  ( ( ( ph  \/  ps )  ->  ( ph  \/  ch ) )  ->  ( ph  \/  ( ps  ->  ch ) ) )

Proof of Theorem pm2.85
StepHypRef Expression
1 orimdi 820 . 2  |-  ( (
ph  \/  ( ps  ->  ch ) )  <->  ( ( ph  \/  ps )  -> 
( ph  \/  ch ) ) )
21biimpri 197 1  |-  ( ( ( ph  \/  ps )  ->  ( ph  \/  ch ) )  ->  ( ph  \/  ( ps  ->  ch ) ) )
Colors of variables: wff set class
Syntax hints:    -> wi 4    \/ wo 357
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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