Theorem pm3.1

Description: Theorem *3.1 of WhiteheadRussell p. 111. (Contributed by NM, 3-Jan-2005)

	Ref	Expression
Assertion	pm3.1	$$⊢\left(\phi \wedge \psi \right)\to \neg \left(\neg \phi \vee \neg \psi \right)$$

Proof

Step	Hyp	Ref	Expression
1		anor	$$⊢\left(\phi \wedge \psi \right)\leftrightarrow \neg \left(\neg \phi \vee \neg \psi \right)$$
2	1	biimpi	$$⊢\left(\phi \wedge \psi \right)\to \neg \left(\neg \phi \vee \neg \psi \right)$$