Theorem pm3.2im

Description: Theorem *3.2 of WhiteheadRussell p. 111, expressed with primitive connectives (see pm3.2 ). (Contributed by NM, 29-Dec-1992) (Proof shortened by Josh Purinton, 29-Dec-2000)

	Ref	Expression
Assertion	pm3.2im	$$⊢\phi \to \left(\psi \to \neg \left(\phi \to \neg \psi \right)\right)$$

Proof

Step	Hyp	Ref	Expression
1		pm2.27	$$⊢\phi \to \left(\left(\phi \to \neg \psi \right)\to \neg \psi \right)$$
2	1	con2d	$$⊢\phi \to \left(\psi \to \neg \left(\phi \to \neg \psi \right)\right)$$