Metamath Proof Explorer


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 ψ φ ψ χ
Assertion pm2.43a ψ φ χ

Proof

Step Hyp Ref Expression
1 pm2.43a.1 ψ φ ψ χ
2 id ψ ψ
3 2 1 mpid ψ φ χ