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Theorem pm2.13 897
Description: Theorem *2.13 of [WhiteheadRussell] p. 101. (Contributed by NM, 3-Jan-2005.)
Assertion
Ref Expression
pm2.13 (𝜑 ∨ ¬ ¬ ¬ 𝜑)

Proof of Theorem pm2.13
StepHypRef Expression
1 notnot 144 . 2 𝜑 → ¬ ¬ ¬ 𝜑)
21orri 861 1 (𝜑 ∨ ¬ ¬ ¬ 𝜑)
Colors of variables: wff setvar class
Syntax hints:  ¬ wn 3  wo 846
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 210  df-or 847
This theorem is referenced by: (None)
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