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Theorem pm2.13 407
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 notnot1 114 . 2 φ → ¬ ¬ ¬ φ)
21orri 365 1 (φ ¬ ¬ ¬ φ)
Colors of variables: wff setvar class
Syntax hints:  ¬ wn 3   wo 357
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 177  df-or 359
This theorem is referenced by: (None)
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