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Theorem axfrege28 37020
Description: Contraposition. Identical to con3 147. Theorem *2.16 of [WhiteheadRussell] p. 103. (Contributed by RP, 24-Dec-2019.)
Assertion
Ref Expression
axfrege28 ((𝜑𝜓) → (¬ 𝜓 → ¬ 𝜑))

Proof of Theorem axfrege28
StepHypRef Expression
1 con3 147 1 ((𝜑𝜓) → (¬ 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: (None)
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