Theorem pm4.62

Description: Theorem *4.62 of WhiteheadRussell p. 120. (Contributed by NM, 3-Jan-2005)

	Ref	Expression
Assertion	pm4.62	$$⊢\left(\phi \to \neg \psi \right)\leftrightarrow \left(\neg \phi \vee \neg \psi \right)$$

Proof

Step	Hyp	Ref	Expression
1		imor	$$⊢\left(\phi \to \neg \psi \right)\leftrightarrow \left(\neg \phi \vee \neg \psi \right)$$