Theorem pm2.3

Description: Theorem *2.3 of WhiteheadRussell p. 104. (Contributed by NM, 3-Jan-2005)

	Ref	Expression
Assertion	pm2.3	$$⊢\left(\phi \vee \left(\psi \vee \chi \right)\right)\to \left(\phi \vee \left(\chi \vee \psi \right)\right)$$

Proof

Step	Hyp	Ref	Expression
1		pm1.4	$$⊢\left(\psi \vee \chi \right)\to \left(\chi \vee \psi \right)$$
2	1	orim2i	$$⊢\left(\phi \vee \left(\psi \vee \chi \right)\right)\to \left(\phi \vee \left(\chi \vee \psi \right)\right)$$