Theorem pm2.43a

Description: Inference absorbing redundant antecedent. (Contributed by NM, 7-Nov-1995) (Proof shortened by Mel L. O'Cat, 28-Nov-2008)

	Ref	Expression
Hypothesis	pm2.43a.1	$$⊢\psi \to \left(\phi \to \left(\psi \to \chi \right)\right)$$
Assertion	pm2.43a	$$⊢\psi \to \left(\phi \to \chi \right)$$

Proof

Step	Hyp	Ref	Expression
1		pm2.43a.1	$$⊢\psi \to \left(\phi \to \left(\psi \to \chi \right)\right)$$
2		id	$$⊢\psi \to \psi$$
3	2 1	mpid	$$⊢\psi \to \left(\phi \to \chi \right)$$