Theorem pm2.26

Description: Theorem *2.26 of WhiteheadRussell p. 104. See pm2.27 . (Contributed by NM, 3-Jan-2005) (Proof shortened by Wolf Lammen, 23-Nov-2012)

	Ref	Expression
Assertion	pm2.26	$$⊢\left(\neg \phi \vee \left(\left(\phi \to \psi \right)\to \psi \right)\right)$$

Proof

Step	Hyp	Ref	Expression
1		pm2.27	$$⊢\phi \to \left(\left(\phi \to \psi \right)\to \psi \right)$$
2	1	imori	$$⊢\left(\neg \phi \vee \left(\left(\phi \to \psi \right)\to \psi \right)\right)$$