Theorem mth8 123

Description: Theorem 8 of [Margaris] p. 60. (The proof was 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 62	. 2 ⊢ (φ → ((φ → ψ) → ψ))
2	1	con3d 95	1 ⊢ (φ → (¬ ψ → ¬ (φ → ψ)))

Syntax hints:  ¬ wn 2   → wi 3

This theorem was proved from axioms:  ax-1 4  ax-2 5  ax-3 6  ax-mp 7

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