Theorem pm2.4

Description: Theorem *2.4 of WhiteheadRussell p. 106. (Contributed by NM, 3-Jan-2005)

	Ref	Expression
Assertion	pm2.4	$$⊢\left(\phi \vee \left(\phi \vee \psi \right)\right)\to \left(\phi \vee \psi \right)$$

Proof

Step	Hyp	Ref	Expression
1		orc	$$⊢\phi \to \left(\phi \vee \psi \right)$$
2		id	$$⊢\left(\phi \vee \psi \right)\to \left(\phi \vee \psi \right)$$
3	1 2	jaoi	$$⊢\left(\phi \vee \left(\phi \vee \psi \right)\right)\to \left(\phi \vee \psi \right)$$