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Theorem 4exmid 939
Description: The disjunction of the four possible combinations of two wffs and their negations is always true. (Contributed by David Abernethy, 28-Jan-2014.)
Assertion
Ref Expression
4exmid

Proof of Theorem 4exmid
StepHypRef Expression
1 exmid 415 . 2
2 dfbi3 893 . . 3
3 xor 891 . . 3
42, 3orbi12i 521 . 2
51, 4mpbi 208 1
Colors of variables: wff setvar class
Syntax hints:  -.wn 3  <->wb 184  \/wo 368  /\wa 369
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
  Copyright terms: Public domain W3C validator