Theorem simprim

Description: Simplification. Similar to Theorem *3.27 (Simp) of WhiteheadRussell p. 112. (Contributed by NM, 3-Jan-1993) (Proof shortened by Wolf Lammen, 13-Nov-2012)

	Ref	Expression
Assertion	simprim	$$⊢\neg \left(\phi \to \neg \psi \right)\to \psi$$

Proof

Step	Hyp	Ref	Expression
1		idd	$$⊢\phi \to \left(\psi \to \psi \right)$$
2	1	impi	$$⊢\neg \left(\phi \to \neg \psi \right)\to \psi$$