Theorem 2false 691

Description: Two falsehoods are equivalent. (Contributed by NM, 4-Apr-2005.) (Revised by Mario Carneiro, 31-Jan-2015.)

Hypotheses

Ref	Expression
2false.1	|- -. ph
2false.2	|- -. ps

Assertion

Ref	Expression
2false	|- ( ph <-> ps )

Proof of Theorem 2false

Step	Hyp	Ref	Expression
1		2false.1	. . 3 |- -. ph
2	1	pm2.21i 636	. 2 |- ( ph -> ps )
3		2false.2	. . 3 |- -. ps
4	3	pm2.21i 636	. 2 |- ( ps -> ph )
5	2, 4	impbii 125	1 |- ( ph <-> ps )

Syntax hints:   -. wn 3   <-> wb 104

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

This theorem depends on definitions:  df-bi 116

This theorem is referenced by:  bianfi  932  bifal  1345  dfnul2  3370  dfnul3  3371  rab0  3396  iun0  3877  0iun  3878  0xp  4627  cnv0  4950  co02  5060  0er  6471  bdnth  13203  bdnthALT  13204