Theorem pm2.53

Description: Theorem *2.53 of WhiteheadRussell p. 107. (Contributed by NM, 3-Jan-2005)

	Ref	Expression
Assertion	pm2.53	$$⊢\left(\phi \vee \psi \right)\to \left(\neg \phi \to \psi \right)$$

Proof

Step	Hyp	Ref	Expression
1		df-or	$$⊢\left(\phi \vee \psi \right)\leftrightarrow \left(\neg \phi \to \psi \right)$$
2	1	biimpi	$$⊢\left(\phi \vee \psi \right)\to \left(\neg \phi \to \psi \right)$$