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Theorem pm3.1 484
Description: Theorem *3.1 of [WhiteheadRussell] p. 111. (Contributed by NM, 3-Jan-2005.)
Assertion
Ref Expression
pm3.1 ((φ ψ) → ¬ (¬ φ ¬ ψ))

Proof of Theorem pm3.1
StepHypRef Expression
1 anor 475 . 2 ((φ ψ) ↔ ¬ (¬ φ ¬ ψ))
21biimpi 186 1 ((φ ψ) → ¬ (¬ φ ¬ ψ))
Colors of variables: wff setvar class
Syntax hints:  ¬ wn 3  wi 4   wo 357   wa 358
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  df-an 360
This theorem is referenced by:  pm3.14  488
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