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Theorem pm2.8 823
Description: Theorem *2.8 of [WhiteheadRussell] p. 108. (Contributed by NM, 3-Jan-2005.) (Proof shortened by Wolf Lammen, 5-Jan-2013.)
Assertion
Ref Expression
pm2.8  |-  ( (
ph  \/  ps )  ->  ( ( -.  ps  \/  ch )  ->  ( ph  \/  ch ) ) )

Proof of Theorem pm2.8
StepHypRef Expression
1 pm2.53 362 . . 3  |-  ( (
ph  \/  ps )  ->  ( -.  ph  ->  ps ) )
21con1d 116 . 2  |-  ( (
ph  \/  ps )  ->  ( -.  ps  ->  ph ) )
32orim1d 812 1  |-  ( (
ph  \/  ps )  ->  ( ( -.  ps  \/  ch )  ->  ( ph  \/  ch ) ) )
Colors of variables: wff set class
Syntax hints:   -. wn 3    -> 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  df-an 360
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