Metamath Proof Explorer

Theorem axfrege28

Description: Contraposition. Identical to con3 . Theorem *2.16 of WhiteheadRussell p. 103. (Contributed by RP, 24-Dec-2019)

Ref Expression
Assertion axfrege28 ( ( 𝜑 → 𝜓 ) → ( ¬ 𝜓 → ¬ 𝜑 ) )

Proof

Step Hyp Ref Expression
1 con3 ⊢ ( ( 𝜑 → 𝜓 ) → ( ¬ 𝜓 → ¬ 𝜑 ) )