Theorem mth8 138

Description: Theorem 8 of [Margaris] p. 60. (Contributed by NM, 5-Aug-1993.) (Proof shortened by Josh Purinton, 29-Dec-2000.)

Assertion

Ref	Expression
mth8	⊢ (φ → (¬ ψ → ¬ (φ → ψ)))

Proof of Theorem mth8

Step	Hyp	Ref	Expression
1		pm2.27 35	. 2 ⊢ (φ → ((φ → ψ) → ψ))
2	1	con3d 125	1 ⊢ (φ → (¬ ψ → ¬ (φ → ψ)))

Syntax hints:  ¬ wn 3   → wi 4

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8

This theorem is referenced by: (None)