Theorem pm2.36

Description: Theorem *2.36 of WhiteheadRussell p. 105. (Contributed by NM, 6-Mar-2008)

	Ref	Expression
Assertion	pm2.36	$$⊢\left(\psi \to \chi \right)\to \left(\left(\phi \vee \psi \right)\to \left(\chi \vee \phi \right)\right)$$

Proof

Step	Hyp	Ref	Expression
1		pm1.4	$$⊢\left(\phi \vee \psi \right)\to \left(\psi \vee \phi \right)$$
2		pm2.38	$$⊢\left(\psi \to \chi \right)\to \left(\left(\psi \vee \phi \right)\to \left(\chi \vee \phi \right)\right)$$
3	1 2	syl5	$$⊢\left(\psi \to \chi \right)\to \left(\left(\phi \vee \psi \right)\to \left(\chi \vee \phi \right)\right)$$