Theorem bicom 140

Description: Commutative law for equivalence. Theorem *4.21 of [WhiteheadRussell] p. 117. (Contributed by NM, 5-Aug-1993.) (Revised by NM, 11-Nov-2012.)

Assertion

Ref	Expression
bicom	|- ( ( ph <-> ps ) <-> ( ps <-> ph ) )

Proof of Theorem bicom

Step	Hyp	Ref	Expression
1		bicom1 131	. 2 |- ( ( ph <-> ps ) -> ( ps <-> ph ) )
2		bicom1 131	. 2 |- ( ( ps <-> ph ) -> ( ph <-> ps ) )
3	1, 2	impbii 126	1 |- ( ( ph <-> ps ) <-> ( ps <-> ph ) )

Syntax hints:   <-> wb 105

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-ia1 106  ax-ia2 107  ax-ia3 108

This theorem depends on definitions:  df-bi 117

This theorem is referenced by:  bicomd  141  bibi1i  228  bibi1d  233  ibibr  246  bibif  703  con2bidc  880  con2biddc  885  pm5.17dc  909  bigolden  961  nbbndc  1436  bilukdc  1438  falbitru  1459  3impexpbicom  1481  exists1  2174  eqcom  2231  abeq1  2339  necon2abiddc  2466  necon2bbiddc  2467  necon4bbiddc  2474  ssequn1  3374  axpow3  4261  isocnv  5935  suplocsrlem  7995  uzennn  10658  bezoutlemle  12529