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Theorem pm4.64 361
Description: Theorem *4.64 of [WhiteheadRussell] p. 120. (Contributed by NM, 3-Jan-2005.)
Assertion
Ref Expression
pm4.64 ((¬ φψ) ↔ (φ ψ))

Proof of Theorem pm4.64
StepHypRef Expression
1 df-or 359 . 2 ((φ ψ) ↔ (¬ φψ))
21bicomi 193 1 ((¬ φψ) ↔ (φ ψ))
Colors of variables: wff setvar class
Syntax hints:  ¬ wn 3  wi 4  wb 176   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:  pm4.66  409  ioran  476
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