Theorem pm1.4

Description: Axiom *1.4 of WhiteheadRussell p. 96. (Contributed by NM, 3-Jan-2005)

	Ref	Expression
Assertion	pm1.4	$$⊢\left(\phi \vee \psi \right)\to \left(\psi \vee \phi \right)$$

Proof

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