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Theorem pm2.52 147
Description: Theorem *2.52 of [WhiteheadRussell] p. 107. (Contributed by NM, 3-Jan-2005.) (Proof shortened by Wolf Lammen, 8-Oct-2012.)
Assertion
Ref Expression
pm2.52  |-  ( -.  ( ph  ->  ps )  ->  ( -.  ph  ->  -.  ps ) )

Proof of Theorem pm2.52
StepHypRef Expression
1 pm2.521 146 . 2  |-  ( -.  ( ph  ->  ps )  ->  ( ps  ->  ph ) )
21con3d 125 1  |-  ( -.  ( ph  ->  ps )  ->  ( -.  ph  ->  -.  ps ) )
Colors of variables: wff set class
Syntax hints:   -. wn 3    -> wi 4
This theorem was proved from axioms:  ax-1 5  ax-2 6  ax-3 7  ax-mp 8
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