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Theorem pm2.8 826
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 pm2.53 364 . . 3  |-  ( (
ph  \/  ps )  ->  ( -.  ph  ->  ps ) )
21con1d 118 . 2  |-  ( (
ph  \/  ps )  ->  ( -.  ps  ->  ph ) )
32orim1d 815 1  |-  ( (
ph  \/  ps )  ->  ( ( -.  ps  \/  ch )  ->  ( ph  \/  ch ) ) )
Colors of variables: wff set class
Syntax hints:   -. wn 5    -> wi 6    \/ wo 359
This theorem was proved from axioms:  ax-1 7  ax-2 8  ax-3 9  ax-mp 10
This theorem depends on definitions:  df-bi 179  df-or 361  df-an 362
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