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Theorem pm2.52 165
Description: Theorem *2.52 of [WhiteheadRussell] p. 107. (Contributed by NM, 3-Jan-2005.) (Proof shortened by Wolf Lammen, 8-Oct-2012.)
Assertion
Ref Expression
pm2.52 (¬ (𝜑𝜓) → (¬ 𝜑 → ¬ 𝜓))

Proof of Theorem pm2.52
StepHypRef Expression
1 pm2.521 164 . 2 (¬ (𝜑𝜓) → (𝜓𝜑))
21con3d 146 1 (¬ (𝜑𝜓) → (¬ 𝜑 → ¬ 𝜓))
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: (None)
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