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Theorem pm4.64 848
Description: Theorem *4.64 of [WhiteheadRussell] p. 120. (Contributed by NM, 3-Jan-2005.)
Assertion
Ref Expression
pm4.64 ((¬ 𝜑𝜓) ↔ (𝜑𝜓))

Proof of Theorem pm4.64
StepHypRef Expression
1 df-or 847 . 2 ((𝜑𝜓) ↔ (¬ 𝜑𝜓))
21bicomi 227 1 ((¬ 𝜑𝜓) ↔ (𝜑𝜓))
Colors of variables: wff setvar class
Syntax hints:  ¬ wn 3  wi 4  wb 209  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:  pm4.66  849  ioran  983  dfifp3  1065  fimaxg  8839  fiming  9035  kmlem8  9657  axgroth6  10328  dfconn2  22170  ifpimimb  40665  ifpor123g  40669  hirstL-ax3  43926
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