Theorem pm3.27im 121

Description: Simplification. Similar to Theorem *3.27 of [WhiteheadRussell] p. 112.

Assertion

Ref	Expression
pm3.27im	⊢ (¬ (φ → ¬ ψ) → ψ)

Proof of Theorem pm3.27im

Step	Hyp	Ref	Expression
1		ax-1 3	. 2 ⊢ (¬ ψ → (φ → ¬ ψ))
2	1	con1i 88	1 ⊢ (¬ (φ → ¬ ψ) → ψ)

Syntax hints:  ¬ wn 1   → wi 2

This theorem is referenced by:  bi2 131  bi3 132  pm3.27 260

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

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