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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 ((φ → ¬ ψ) → (ψ → ¬ φ))

Proof of Theorem con2
StepHypRef Expression
1 id 19 . 2 ((φ → ¬ ψ) → (φ → ¬ ψ))
21con2d 107 1 ((φ → ¬ ψ) → (ψ → ¬ φ))
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:  con2b  324  sp  1747  spOLD  1748
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