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Theorem pm3.11 986
Description: Theorem *3.11 of [WhiteheadRussell] p. 111. (Contributed by NM, 3-Jan-2005.)
Assertion
Ref Expression
pm3.11 (¬ (¬ 𝜑 ∨ ¬ 𝜓) → (𝜑𝜓))

Proof of Theorem pm3.11
StepHypRef Expression
1 anor 976 . 2 ((𝜑𝜓) ↔ ¬ (¬ 𝜑 ∨ ¬ 𝜓))
21biimpri 229 1 (¬ (¬ 𝜑 ∨ ¬ 𝜓) → (𝜑𝜓))
Colors of variables: wff setvar class
Syntax hints:  ¬ wn 3  wi 4  wa 396  wo 841
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 208  df-an 397  df-or 842
This theorem is referenced by:  pm3.12  987  pm3.13  988  ecased  1027
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