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Theorem pm2.49 390
Description: Theorem *2.49 of [WhiteheadRussell] p. 107. (Contributed by NM, 3-Jan-2005.)
Assertion
Ref Expression
pm2.49 (¬ (φ ψ) → (¬ φ ¬ ψ))

Proof of Theorem pm2.49
StepHypRef Expression
1 pm2.46 387 . 2 (¬ (φ ψ) → ¬ ψ)
21olcd 382 1 (¬ (φ ψ) → (¬ φ ¬ ψ))
Colors of variables: wff setvar class
Syntax hints:  ¬ wn 3  wi 4   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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