Theorem nbfal 1254

Description: The negation of a proposition is equivalent to itself being equivalent to F.. (Contributed by Anthony Hart, 14-Aug-2011.)

Assertion

Ref	Expression
nbfal	|- ( -. ph <-> ( ph <-> F. ) )

Proof of Theorem nbfal

Step	Hyp	Ref	Expression
1		fal 1250	. 2 |- -. F.
2	1	nbn 615	1 |- ( -. ph <-> ( ph <-> F. ) )

Syntax hints:   -. wn 3   <-> wb 98   F. wfal 1248

This theorem was proved from axioms:  ax-1 5  ax-2 6  ax-mp 7  ax-ia1 99  ax-ia2 100  ax-ia3 101  ax-in1 544  ax-in2 545

This theorem depends on definitions:  df-bi 110  df-tru 1246  df-fal 1249

This theorem is referenced by:  zfnuleu  3881