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Theorem impi 140
Description: An importation inference. (Contributed by NM, 5-Aug-1993.) (Proof shortened by Wolf Lammen, 20-Jul-2013.)
Hypothesis
Ref Expression
impi.1 (φ → (ψχ))
Assertion
Ref Expression
impi (¬ (φ → ¬ ψ) → χ)

Proof of Theorem impi
StepHypRef Expression
1 impi.1 . . 3 (φ → (ψχ))
21con3rr3 128 . 2 χ → (φ → ¬ ψ))
32con1i 121 1 (¬ (φ → ¬ ψ) → χ)
Colors of variables: wff setvar class
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:  simprim  142  dfbi1  184  imp  418
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