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  700  con2bidc  877  con2biddc  882  pm5.17dc  906  bigolden  958  nbbndc  1414  bilukdc  1416  falbitru  1437  3impexpbicom  1459  exists1  2152  eqcom  2209  abeq1  2317  necon2abiddc  2444  necon2bbiddc  2445  necon4bbiddc  2452  ssequn1  3351  axpow3  4237  isocnv  5903  suplocsrlem  7956  uzennn  10618  bezoutlemle  12444