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Theorem con1 122
Description: Contraposition. Theorem *2.15 of [WhiteheadRussell] p. 102. (Contributed by NM, 5-Aug-1993.) (Proof shortened by Wolf Lammen, 12-Feb-2013.)
Assertion
Ref Expression
con1  |-  ( ( -.  ph  ->  ps )  ->  ( -.  ps  ->  ph ) )

Proof of Theorem con1
StepHypRef Expression
1 id 21 . 2  |-  ( ( -.  ph  ->  ps )  ->  ( -.  ph  ->  ps ) )
21con1d 118 1  |-  ( ( -.  ph  ->  ps )  ->  ( -.  ps  ->  ph ) )
Colors of variables: wff set class
Syntax hints:   -. wn 5    -> wi 6
This theorem is referenced by:  con1b  325  ax12olem23  1657  nneob  6583  uzwo  10213  uzwoOLD  10214  ax12olem23aK  28206  ax12olem23X  28207
This theorem was proved from axioms:  ax-1 7  ax-2 8  ax-3 9  ax-mp 10
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