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Theorem con2 108
Description: Contraposition. Theorem *2.03 of [WhiteheadRussell] p. 100. (Contributed by NM, 5-Aug-1993.) (Proof shortened by Wolf Lammen, 12-Feb-2013.)
Assertion
Ref Expression
con2  |-  ( (
ph  ->  -.  ps )  ->  ( ps  ->  -.  ph ) )

Proof of Theorem con2
StepHypRef Expression
1 id 19 . 2  |-  ( (
ph  ->  -.  ps )  ->  ( ph  ->  -.  ps ) )
21con2d 107 1  |-  ( (
ph  ->  -.  ps )  ->  ( ps  ->  -.  ph ) )
Colors of variables: wff set class
Syntax hints:   -. wn 3    -> wi 4
This theorem is referenced by:  con2b  324  sp  1716  isprm5  12791  ax9lem3  29142
This theorem was proved from axioms:  ax-1 5  ax-2 6  ax-3 7  ax-mp 8
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