Theorem bibif 688

Description: Transfer negation via an equivalence. (Contributed by NM, 3-Oct-2007.) (Proof shortened by Wolf Lammen, 28-Jan-2013.)

Assertion

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

Proof of Theorem bibif

Step	Hyp	Ref	Expression
1		nbn2 687	. 2 |- ( -. ps -> ( -. ph <-> ( ps <-> ph ) ) )
2		bicom 139	. 2 |- ( ( ps <-> ph ) <-> ( ph <-> ps ) )
3	1, 2	bitr2di 196	1 |- ( -. ps -> ( ( ph <-> ps ) <-> -. ph ) )

Syntax hints:   -. wn 3   -> wi 4   <-> wb 104

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-ia1 105  ax-ia2 106  ax-ia3 107  ax-in1 604  ax-in2 605

This theorem depends on definitions:  df-bi 116

This theorem is referenced by:  nbn  689