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Theorem falbifal 1671
Description: A identity. (Contributed by Anthony Hart, 22-Oct-2010.) (Proof shortened by Andrew Salmon, 13-May-2011.)
Assertion
Ref Expression
falbifal ((⊥ ↔ ⊥) ↔ ⊤)

Proof of Theorem falbifal
StepHypRef Expression
1 biid 251 . 2 (⊥ ↔ ⊥)
21bitru 1644 1 ((⊥ ↔ ⊥) ↔ ⊤)
Colors of variables: wff setvar class
Syntax hints:  wb 196  wtru 1632  wfal 1636
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 197  df-tru 1634
This theorem is referenced by:  falxorfal  1679
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