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Theorem norbi 859
Description: If neither of two propositions is true, then these propositions are equivalent. (Contributed by BJ, 26-Apr-2019.)
Assertion
Ref Expression
norbi

Proof of Theorem norbi
StepHypRef Expression
1 orc 385 . 2
2 olc 384 . 2
31, 2pm5.21ni 352 1
Colors of variables: wff setvar class
Syntax hints:  -.wn 3  ->wi 4  <->wb 184  \/wo 368
This theorem is referenced by:  nbior  860  oibabs  881
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
  Copyright terms: Public domain W3C validator