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Theorem con1 128
Description: Contraposition. Theorem *2.15 of [WhiteheadRussell] p. 102. (Contributed by NM, 29-Dec-1992.) (Proof shortened by Wolf Lammen, 12-Feb-2013.)
Assertion
Ref Expression
con1  |-  ( ( -.  ph  ->  ps )  ->  ( -.  ps  ->  ph ) )

Proof of Theorem con1
StepHypRef Expression
1 id 22 . 2  |-  ( ( -.  ph  ->  ps )  ->  ( -.  ph  ->  ps ) )
21con1d 124 1  |-  ( ( -.  ph  ->  ps )  ->  ( -.  ps  ->  ph ) )
Colors of variables: wff setvar class
Syntax hints:   -. wn 3    -> wi 4
This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8
This theorem is referenced by:  con1b  333  nneob  7194  uzwo  11021  uzwoOLD  11022
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