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Theorem con3 553
Description: Contraposition. Theorem *2.16 of [WhiteheadRussell] p. 103. (Contributed by NM, 5-Aug-1993.) (Proof shortened by Wolf Lammen, 13-Feb-2013.)
Assertion
Ref Expression
con3 ((φψ) → (¬ ψ → ¬ φ))

Proof of Theorem con3
StepHypRef Expression
1 id 17 . 2 ((φψ) → (φψ))
21con3d 544 1 ((φψ) → (¬ ψ → ¬ φ))
Colors of variables: wff set class
Syntax hints:  ¬ wn 3  wi 4
This theorem is referenced by:  mtt  592  con34bdc  741  annimim  758  hbnt  1486  ralf0  3204
This theorem was proved from axioms:  ax-1 5  ax-2 6  ax-mp 7  ax-in1 528  ax-in2 529
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