Theorem pm2.5g

Description: General instance of Theorem *2.5 of WhiteheadRussell p. 107. (Contributed by NM, 3-Jan-2005) (Proof shortened by Wolf Lammen, 9-Oct-2012)

	Ref	Expression
Assertion	pm2.5g	$$⊢\neg \left(\phi \to \psi \right)\to \left(\neg \phi \to \chi \right)$$

Proof

Step	Hyp	Ref	Expression
1		simplim	$$⊢\neg \left(\phi \to \psi \right)\to \phi$$
2	1	pm2.24d	$$⊢\neg \left(\phi \to \psi \right)\to \left(\neg \phi \to \chi \right)$$