Theorem trubitru 1569

Description: A ↔ identity. (Contributed by Anthony Hart, 22-Oct-2010.) (Proof shortened by Andrew Salmon, 13-May-2011.)

Assertion

Ref	Expression
trubitru	⊢ ((⊤ ↔ ⊤) ↔ ⊤)

Proof of Theorem trubitru

Step	Hyp	Ref	Expression
1		biid 261	. 2 ⊢ (⊤ ↔ ⊤)
2	1	bitru 1549	1 ⊢ ((⊤ ↔ ⊤) ↔ ⊤)

Syntax hints:   ↔ wb 206  ⊤wtru 1541

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 207  df-tru 1543

This theorem is referenced by:  truxortru  1585