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Theorem pm4.57 518
Description: Theorem *4.57 of [WhiteheadRussell] p. 120. (Contributed by NM, 3-Jan-2005.)
Assertion
Ref Expression
pm4.57 (¬ (¬ 𝜑 ∧ ¬ 𝜓) ↔ (𝜑𝜓))

Proof of Theorem pm4.57
StepHypRef Expression
1 oran 517 . 2 ((𝜑𝜓) ↔ ¬ (¬ 𝜑 ∧ ¬ 𝜓))
21bicomi 214 1 (¬ (¬ 𝜑 ∧ ¬ 𝜓) ↔ (𝜑𝜓))
Colors of variables: wff setvar class
Syntax hints:  ¬ wn 3  wb 196  wo 383  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-or 385  df-an 386
This theorem is referenced by:  gcdaddmlem  15169  arg-ax  32054  tsbi2  33570
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