Theorem pm2.25

Description: Theorem *2.25 of WhiteheadRussell p. 104. (Contributed by NM, 3-Jan-2005)

	Ref	Expression
Assertion	pm2.25	$$⊢\left(\phi \vee \left(\left(\phi \vee \psi \right)\to \psi \right)\right)$$

Proof

Step	Hyp	Ref	Expression
1		orel1	$$⊢\neg \phi \to \left(\left(\phi \vee \psi \right)\to \psi \right)$$
2	1	orri	$$⊢\left(\phi \vee \left(\left(\phi \vee \psi \right)\to \psi \right)\right)$$