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Theorem pm4.63 437
Description: Theorem *4.63 of [WhiteheadRussell] p. 120. (Contributed by NM, 3-Jan-2005.)
Assertion
Ref Expression
pm4.63 (¬ (𝜑 → ¬ 𝜓) ↔ (𝜑𝜓))

Proof of Theorem pm4.63
StepHypRef Expression
1 df-an 386 . 2 ((𝜑𝜓) ↔ ¬ (𝜑 → ¬ 𝜓))
21bicomi 214 1 (¬ (𝜑 → ¬ 𝜓) ↔ (𝜑𝜓))
Colors of variables: wff setvar class
Syntax hints:  ¬ wn 3  wi 4  wb 196  wa 384
This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8
This theorem depends on definitions:  df-bi 197  df-an 386
This theorem is referenced by:  pm4.67  444  nqereu  9702  axacprim  31319  andnand1  32067
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