Theorem nbfal 1295

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 1291	. 2 |- -. F.
2	1	nbn 647	1 |- ( -. ph <-> ( ph <-> F. ) )

Syntax hints:   -. wn 3   <-> wb 103   F. wfal 1289

This theorem was proved from axioms:  ax-1 5  ax-2 6  ax-mp 7  ax-ia1 104  ax-ia2 105  ax-ia3 106  ax-in1 576  ax-in2 577

This theorem depends on definitions:  df-bi 115  df-tru 1287  df-fal 1290

This theorem is referenced by:  zfnuleu  3902