Theorem bj-notbi 10716

Description: Equivalence property for negation. TODO: minimize all theorems using notbid 624 and notbii 626. (Contributed by BJ, 27-Jan-2020.) (Proof modification is discouraged.)

Assertion

Ref	Expression
bj-notbi	|- ( ( ph <-> ps ) -> ( -. ph <-> -. ps ) )

Proof of Theorem bj-notbi

Step	Hyp	Ref	Expression
1		bi2 128	. . 3 |- ( ( ph <-> ps ) -> ( ps -> ph ) )
2	1	con3d 593	. 2 |- ( ( ph <-> ps ) -> ( -. ph -> -. ps ) )
3		bi1 116	. . 3 |- ( ( ph <-> ps ) -> ( ph -> ps ) )
4	3	con3d 593	. 2 |- ( ( ph <-> ps ) -> ( -. ps -> -. ph ) )
5	2, 4	impbid 127	1 |- ( ( ph <-> ps ) -> ( -. ph <-> -. ps ) )

Syntax hints:   -. wn 3   -> wi 4   <-> 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:  bj-notbii  10717  bj-notbid  10718  bj-dcbi  10719