Theorem orim2

Description: Axiom *1.6 (Sum) of WhiteheadRussell p. 97. (Contributed by NM, 3-Jan-2005)

	Ref	Expression
Assertion	orim2	$$⊢\left(\psi \to \chi \right)\to \left(\left(\phi \vee \psi \right)\to \left(\phi \vee \chi \right)\right)$$

Proof

Step	Hyp	Ref	Expression
1		id	$$⊢\left(\psi \to \chi \right)\to \left(\psi \to \chi \right)$$
2	1	orim2d	$$⊢\left(\psi \to \chi \right)\to \left(\left(\phi \vee \psi \right)\to \left(\phi \vee \chi \right)\right)$$