Theorem fal 1349

Description: The truth value F. is refutable. (Contributed by Anthony Hart, 22-Oct-2010.) (Proof shortened by Mel L. O'Cat, 11-Mar-2012.)

Assertion

Ref	Expression
fal	|- -. F.

Proof of Theorem fal

Step	Hyp	Ref	Expression
1		tru 1346	. . 3 |- T.
2	1	notnoti 635	. 2 |- -. -. T.
3		df-fal 1348	. 2 |- ( F. <-> -. T. )
4	2, 3	mtbir 661	1 |- -. F.

Syntax hints:   -. wn 3   T. wtru 1343   F. wfal 1347

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-ia1 105  ax-ia2 106  ax-ia3 107  ax-in1 604  ax-in2 605

This theorem depends on definitions:  df-bi 116  df-tru 1345  df-fal 1348

This theorem is referenced by:  nbfal  1353  bifal  1355  falim  1356  dfnot  1360  notfal  1403  alnex  1486  csbprc  3449  bj-stfal  13459  bj-dcfal  13469  bdnth  13551