Theorem bibif 614

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 613	. 2 |- ( -. ps -> ( -. ph <-> ( ps <-> ph ) ) )
2		bicom 128	. 2 |- ( ( ps <-> ph ) <-> ( ph <-> ps ) )
3	1, 2	syl6rbb 186	1 |- ( -. ps -> ( ( ph <-> ps ) <-> -. ph ) )

Syntax hints:   -. wn 3   -> wi 4   <-> wb 98

This theorem was proved from axioms:  ax-1 5  ax-2 6  ax-mp 7  ax-ia1 99  ax-ia2 100  ax-ia3 101  ax-in1 544  ax-in2 545

This theorem depends on definitions:  df-bi 110

This theorem is referenced by:  nbn  615