Theorem pm2.64

Description: Theorem *2.64 of WhiteheadRussell p. 107. (Contributed by NM, 3-Jan-2005)

	Ref	Expression
Assertion	pm2.64	$$⊢\left(\phi \vee \psi \right)\to \left(\left(\phi \vee \neg \psi \right)\to \phi \right)$$

Proof

Step	Hyp	Ref	Expression
1		orel2	$$⊢\neg \psi \to \left(\left(\phi \vee \psi \right)\to \phi \right)$$
2	1	jao1i	$$⊢\left(\phi \vee \neg \psi \right)\to \left(\left(\phi \vee \psi \right)\to \phi \right)$$
3	2	com12	$$⊢\left(\phi \vee \psi \right)\to \left(\left(\phi \vee \neg \psi \right)\to \phi \right)$$