Theorem nbn3 723

Description: Transfer falsehood via equivalence.

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	negbi 87	. 2 |- -. -. ph
3	2	nbn 722	1 |- (-. ps <-> (ps <-> -. ph))

Syntax hints:  -. wn 2   <-> wb 146

This theorem is referenced by:  zfnuleu 2707

This theorem was proved from axioms:  ax-1 4  ax-2 5  ax-3 6  ax-mp 7

This theorem depends on definitions:  df-bi 147  df-an 225

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