Theorem nbn3 337

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 115	. 2 |- -. -. ph
3	2	nbn 336	1 |- (-. ps <-> (ps <-> -. ph))

This proof depends on syntax axioms:  -. wn 3   <-> wb 176

This proof depends on axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8

This proof depends on definitions:  df-bi 177

This theorem is used by: (None)