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Theorem pm2.521 148
Description: Theorem *2.521 of [WhiteheadRussell] p. 107. (Contributed by NM, 3-Jan-2005.) (Proof shortened by Wolf Lammen, 8-Oct-2012.)
Assertion
Ref Expression
pm2.521  |-  ( -.  ( ph  ->  ps )  ->  ( ps  ->  ph ) )

Proof of Theorem pm2.521
StepHypRef Expression
1 simplim 145 . 2  |-  ( -.  ( ph  ->  ps )  ->  ph )
21a1d 24 1  |-  ( -.  ( ph  ->  ps )  ->  ( ps  ->  ph ) )
Colors of variables: wff set class
Syntax hints:   -. wn 5    -> wi 6
This theorem is referenced by:  pm2.52  149  loolin  175
This theorem was proved from axioms:  ax-1 7  ax-2 8  ax-3 9  ax-mp 10
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