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Theorem mth8 578
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 → ¬ (φψ)))

Proof of Theorem mth8
StepHypRef Expression
1 pm2.27 35 . 2 (φ → ((φψ) → ψ))
21con3d 560 1 (φ → (¬ ψ → ¬ (φψ)))
Colors of variables: wff set class
Syntax hints:  ¬ wn 3  wi 4
This theorem was proved from axioms:  ax-1 5  ax-2 6  ax-mp 7  ax-in1 544  ax-in2 545
This theorem is referenced by: (None)
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