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Theorem falbitru 1572
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
falbitru ((⊥ ↔ ⊤) ↔ ⊥)

Proof of Theorem falbitru
StepHypRef Expression
1 tbtru 1550 . 2 (⊥ ↔ (⊥ ↔ ⊤))
21bicomi 223 1 ((⊥ ↔ ⊤) ↔ ⊥)
Colors of variables: wff setvar class
Syntax hints:  wb 205  wtru 1543  wfal 1554
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 206  df-tru 1545
This theorem is referenced by:  trubifal  1573
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