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Theorem oran 496
Description: Disjunction in terms of conjunction (De Morgan's law). Compare Theorem *4.57 of [WhiteheadRussell] p. 120. (Contributed by NM, 3-Jan-1993.) (Proof shortened by Andrew Salmon, 7-May-2011.)
Assertion
Ref Expression
oran

Proof of Theorem oran
StepHypRef Expression
1 pm4.56 495 . 2
21con2bii 332 1
Colors of variables: wff setvar class
Syntax hints:  -.wn 3  <->wb 184  \/wo 368  /\wa 369
This theorem is referenced by:  pm4.57  497  nbiorOLD  861  19.43OLD  1694  ordthauslem  19884  mideulem2  24108  opphllem  24109  ordtconlem1  27906  ftc1anclem1  30090  xrlttri5d  31465
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 185  df-or 370  df-an 371
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