Metamath Proof Explorer

Theorem nbfal

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

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

Proof

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