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Theorem pm3.12 989
Description: Theorem *3.12 of [WhiteheadRussell] p. 111. (Contributed by NM, 3-Jan-2005.)
Assertion
Ref Expression
pm3.12 ((¬ 𝜑 ∨ ¬ 𝜓) ∨ (𝜑𝜓))

Proof of Theorem pm3.12
StepHypRef Expression
1 pm3.11 988 . 2 (¬ (¬ 𝜑 ∨ ¬ 𝜓) → (𝜑𝜓))
21orri 858 1 ((¬ 𝜑 ∨ ¬ 𝜓) ∨ (𝜑𝜓))
Colors of variables: wff setvar class
Syntax hints:  ¬ wn 3  wa 396  wo 843
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 844
This theorem is referenced by:  tsan1  35287
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