Theorem pm2.67

Description: Theorem *2.67 of WhiteheadRussell p. 107. (Contributed by NM, 3-Jan-2005)

	Ref	Expression
Assertion	pm2.67	$$⊢\left(\left(\phi \vee \psi \right)\to \psi \right)\to \left(\phi \to \psi \right)$$

Proof

Step	Hyp	Ref	Expression
1		pm2.67-2	$$⊢\left(\left(\phi \vee \psi \right)\to \psi \right)\to \left(\phi \to \psi \right)$$