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Theorem pm2.8 759
Description: Theorem *2.8 of [WhiteheadRussell] p. 108. (Contributed by NM, 3-Jan-2005.) (Proof shortened by Mario Carneiro, 31-Jan-2015.)
Assertion
Ref Expression
pm2.8  |-  ( (
ph  \/  ps )  ->  ( ( -.  ps  \/  ch )  ->  ( ph  \/  ch ) ) )

Proof of Theorem pm2.8
StepHypRef Expression
1 pm1.4 681 . . 3  |-  ( (
ph  \/  ps )  ->  ( ps  \/  ph ) )
21ord 678 . 2  |-  ( (
ph  \/  ps )  ->  ( -.  ps  ->  ph ) )
32orim1d 736 1  |-  ( (
ph  \/  ps )  ->  ( ( -.  ps  \/  ch )  ->  ( ph  \/  ch ) ) )
Colors of variables: wff set class
Syntax hints:   -. wn 3    -> wi 4    \/ wo 664
This theorem was proved from axioms:  ax-1 5  ax-2 6  ax-mp 7  ax-ia1 104  ax-ia2 105  ax-ia3 106  ax-in2 580  ax-io 665
This theorem depends on definitions:  df-bi 115
This theorem is referenced by: (None)
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