Theorem pm2.47

Description: Theorem *2.47 of WhiteheadRussell p. 107. (Contributed by NM, 3-Jan-2005)

	Ref	Expression
Assertion	pm2.47	$$⊢\neg \left(\phi \vee \psi \right)\to \left(\neg \phi \vee \psi \right)$$

Proof

Step	Hyp	Ref	Expression
1		pm2.45	$$⊢\neg \left(\phi \vee \psi \right)\to \neg \phi$$
2	1	orcd	$$⊢\neg \left(\phi \vee \psi \right)\to \left(\neg \phi \vee \psi \right)$$