Theorem pm2.38

Description: Theorem *2.38 of WhiteheadRussell p. 105. (Contributed by NM, 6-Mar-2008)

	Ref	Expression
Assertion	pm2.38	$$⊢\left(\psi \to \chi \right)\to \left(\left(\psi \vee \phi \right)\to \left(\chi \vee \phi \right)\right)$$

Proof

Step	Hyp	Ref	Expression
1		id	$$⊢\left(\psi \to \chi \right)\to \left(\psi \to \chi \right)$$
2	1	orim1d	$$⊢\left(\psi \to \chi \right)\to \left(\left(\psi \vee \phi \right)\to \left(\chi \vee \phi \right)\right)$$