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Axiom ax-frege28 36943
Description: Contraposition. Identical to con3 147. Theorem *2.16 of [WhiteheadRussell] p. 103. Axiom 28 of [Frege1879] p. 43. (Contributed by RP, 24-Dec-2019.) (New usage is discouraged.)
Assertion
Ref Expression
ax-frege28 ((𝜑𝜓) → (¬ 𝜓 → ¬ 𝜑))

Detailed syntax breakdown of Axiom ax-frege28
StepHypRef Expression
1 wph . 2 wff 𝜑
2 wps . 2 wff 𝜓
32wn 3 . . 3 wff ¬ 𝜓
41wn 3 . . 3 wff ¬ 𝜑
53, 4wi 4 . 2 wff 𝜓 → ¬ 𝜑)
61, 2, 5bj-0 31505 1 wff ((𝜑𝜓) → (¬ 𝜓 → ¬ 𝜑))
Colors of variables: wff setvar class
This axiom is referenced by:  frege29  36944  frege33  36949  frege54cor0a  36976
  Copyright terms: Public domain W3C validator