Theorem pm5.13

Description: Theorem *5.13 of WhiteheadRussell p. 123. (Contributed by NM, 3-Jan-2005) (Proof shortened by Wolf Lammen, 14-Nov-2012)

	Ref	Expression
Assertion	pm5.13	$$⊢\left(\left(\phi \to \psi \right)\vee \left(\psi \to \phi \right)\right)$$

Proof

Step	Hyp	Ref	Expression
1		pm5.14	$$⊢\left(\left(\phi \to \psi \right)\vee \left(\psi \to \phi \right)\right)$$