Theorem mth8 108

Description: Theorem 8 of [Margaris] p. 60. (The proof was shortened by Josh Purinton, 29-Dec-00.)

Assertion

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

Proof of Theorem mth8

Step	Hyp	Ref	Expression
1		pm2.27 30	. 2 ⊢ (φ → ((φ → ψ) → ψ))
2	1	con3d 87	1 ⊢ (φ → (¬ ψ → ¬ (φ → ψ)))

Syntax hints:  ¬ wn 1   → wi 2

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

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