Theorem 2false 708

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 651	. 2 |- ( ph -> ps )
3		2false.2	. . 3 |- -. ps
4	3	pm2.21i 651	. 2 |- ( ps -> ph )
5	2, 4	impbii 126	1 |- ( ph <-> ps )

Syntax hints:   -. wn 3   <-> wb 105

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-ia2 107  ax-ia3 108  ax-in2 620

This theorem depends on definitions:  df-bi 117

This theorem is referenced by:  bianfi  955  bifal  1410  dfnul2  3496  dfnul3  3497  rab0  3523  iun0  4027  0iun  4028  0xp  4806  cnv0  5140  co02  5250  0er  6735  2lgslem4  15831  bdnth  16429  bdnthALT  16430