Theorem pm2.43a 45

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

Hypothesis

Ref	Expression
pm2.43a.1	⊢ (ψ → (φ → (ψ → χ)))

Assertion

Ref	Expression
pm2.43a	⊢ (ψ → (φ → χ))

Proof of Theorem pm2.43a

Step	Hyp	Ref	Expression
1		id 19	. 2 ⊢ (ψ → ψ)
2		pm2.43a.1	. 2 ⊢ (ψ → (φ → (ψ → χ)))
3	1, 2	mpid 37	1 ⊢ (ψ → (φ → χ))

Syntax hints:   → wi 4

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7

This theorem is referenced by:  pm2.43b  46  rspc  2950  intss1  3942  ncfin  6248