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Theorem 3orel2 24077
Description: Partial elimination of a triple disjunction by denial of a disjunct. (Contributed by Scott Fenton, 26-Mar-2011.) (Proof shortened by Andrew Salmon, 25-May-2011.)
Assertion
Ref Expression
3orel2  |-  ( -. 
ps  ->  ( ( ph  \/  ps  \/  ch )  ->  ( ph  \/  ch ) ) )

Proof of Theorem 3orel2
StepHypRef Expression
1 3orrot 940 . 2  |-  ( (
ph  \/  ps  \/  ch )  <->  ( ps  \/  ch  \/  ph ) )
2 3orel1 24076 . . 3  |-  ( -. 
ps  ->  ( ( ps  \/  ch  \/  ph )  ->  ( ch  \/  ph ) ) )
3 orcom 376 . . 3  |-  ( ( ch  \/  ph )  <->  (
ph  \/  ch )
)
42, 3syl6ib 217 . 2  |-  ( -. 
ps  ->  ( ( ps  \/  ch  \/  ph )  ->  ( ph  \/  ch ) ) )
51, 4syl5bi 208 1  |-  ( -. 
ps  ->  ( ( ph  \/  ps  \/  ch )  ->  ( ph  \/  ch ) ) )
Colors of variables: wff set class
Syntax hints:   -. wn 3    -> wi 4    \/ wo 357    \/ w3o 933
This theorem is referenced by:  nobnddown  24426
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-3or 935
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