Theorem nbn3 648

Description: Transfer falsehood via equivalence. (Contributed by NM, 11-Sep-2006.)

Hypothesis

Ref	Expression
nbn3.1	|- ph

Assertion

Ref	Expression
nbn3	|- ( -. ps <-> ( ps <-> -. ph ) )

Proof of Theorem nbn3

Step	Hyp	Ref	Expression
1		nbn3.1	. . 3 |- ph
2	1	notnoti 606	. 2 |- -. -. ph
3	2	nbn 647	1 |- ( -. ps <-> ( ps <-> -. ph ) )

Syntax hints:   -. wn 3   <-> wb 103

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

This theorem is referenced by: (None)