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Theorem trubifal 1685
Description: A identity. (Contributed by Anthony Hart, 22-Oct-2010.) (Proof shortened by Andrew Salmon, 13-May-2011.) (Proof shortened by Wolf Lammen, 10-Jul-2020.)
Assertion
Ref Expression
trubifal ((⊤ ↔ ⊥) ↔ ⊥)

Proof of Theorem trubifal
StepHypRef Expression
1 bicom 214 . 2 ((⊤ ↔ ⊥) ↔ (⊥ ↔ ⊤))
2 falbitru 1684 . 2 ((⊥ ↔ ⊤) ↔ ⊥)
31, 2bitri 267 1 ((⊤ ↔ ⊥) ↔ ⊥)
Colors of variables: wff setvar class
Syntax hints:  wb 198  wtru 1654  wfal 1666
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 199  df-tru 1657
This theorem is referenced by:  truxorfal  1700
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