Theorem pm5.12

Description: Theorem *5.12 of WhiteheadRussell p. 123. (Contributed by NM, 3-Jan-2005)

	Ref	Expression
Assertion	pm5.12	$$⊢\left(\left(\phi \to \psi \right)\vee \left(\phi \to \neg \psi \right)\right)$$

Proof

Step	Hyp	Ref	Expression
1		pm2.51	$$⊢\neg \left(\phi \to \psi \right)\to \left(\phi \to \neg \psi \right)$$
2	1	orri	$$⊢\left(\left(\phi \to \psi \right)\vee \left(\phi \to \neg \psi \right)\right)$$