Theorem conax1

Description: Contrapositive of ax-1 . (Contributed by BJ, 28-Oct-2023)

	Ref	Expression
Assertion	conax1	$$⊢\neg \left(\phi \to \psi \right)\to \neg \psi$$

Proof

Step	Hyp	Ref	Expression
1		ax-1	$$⊢\psi \to \left(\phi \to \psi \right)$$
2	1	con3i	$$⊢\neg \left(\phi \to \psi \right)\to \neg \psi$$