Theorem pm2.68

Description: Theorem *2.68 of WhiteheadRussell p. 108. (Contributed by NM, 3-Jan-2005)

	Ref	Expression
Assertion	pm2.68	$$⊢\left(\left(\phi \to \psi \right)\to \psi \right)\to \left(\phi \vee \psi \right)$$

Proof

Step	Hyp	Ref	Expression
1		jarl	$$⊢\left(\left(\phi \to \psi \right)\to \psi \right)\to \left(\neg \phi \to \psi \right)$$
2	1	orrd	$$⊢\left(\left(\phi \to \psi \right)\to \psi \right)\to \left(\phi \vee \psi \right)$$