Theorem grpid 12917

Description: Two ways of saying that an element of a group is the identity element. Provides a convenient way to compute the value of the identity element. (Contributed by NM, 24-Aug-2011.)

Hypotheses

Ref	Expression
grpinveu.b	|- B = ( Base ` G )
grpinveu.p	|- .+ = ( +g ` G )
grpinveu.o	|- .0. = ( 0g ` G )

Assertion

Ref	Expression
grpid	|- ( ( G e. Grp /\ X e. B ) -> ( ( X .+ X ) = X <-> .0. = X ) )

Proof of Theorem grpid

Step	Hyp	Ref	Expression
1		eqcom 2179	. 2 |- ( .0. = X <-> X = .0. )
2		grpinveu.b	. . . . . . 7 |- B = ( Base ` G )
3		grpinveu.o	. . . . . . 7 |- .0. = ( 0g ` G )
4	2, 3	grpidcl 12909	. . . . . 6 |- ( G e. Grp -> .0. e. B )
5		grpinveu.p	. . . . . . . 8 |- .+ = ( +g ` G )
6	2, 5	grprcan 12915	. . . . . . 7 |- ( ( G e. Grp /\ ( X e. B /\ .0. e. B /\ X e. B ) ) -> ( ( X .+ X ) = ( .0. .+ X ) <-> X = .0. ) )
7	6	3exp2 1225	. . . . . 6 |- ( G e. Grp -> ( X e. B -> ( .0. e. B -> ( X e. B -> ( ( X .+ X ) = ( .0. .+ X ) <-> X = .0. ) ) ) ) )
8	4, 7	mpid 42	. . . . 5 |- ( G e. Grp -> ( X e. B -> ( X e. B -> ( ( X .+ X ) = ( .0. .+ X ) <-> X = .0. ) ) ) )
9	8	pm2.43d 50	. . . 4 |- ( G e. Grp -> ( X e. B -> ( ( X .+ X ) = ( .0. .+ X ) <-> X = .0. ) ) )
10	9	imp 124	. . 3 |- ( ( G e. Grp /\ X e. B ) -> ( ( X .+ X ) = ( .0. .+ X ) <-> X = .0. ) )
11	2, 5, 3	grplid 12911	. . . 4 |- ( ( G e. Grp /\ X e. B ) -> ( .0. .+ X ) = X )
12	11	eqeq2d 2189	. . 3 |- ( ( G e. Grp /\ X e. B ) -> ( ( X .+ X ) = ( .0. .+ X ) <-> ( X .+ X ) = X ) )
13	10, 12	bitr3d 190	. 2 |- ( ( G e. Grp /\ X e. B ) -> ( X = .0. <-> ( X .+ X ) = X ) )
14	1, 13	bitr2id 193	1 |- ( ( G e. Grp /\ X e. B ) -> ( ( X .+ X ) = X <-> .0. = X ) )

Syntax hints:   -> wi 4   /\ wa 104   <-> wb 105   = wceq 1353   e. wcel 2148   ` cfv 5218  (class class class)co 5877   Basecbs 12464   +g cplusg 12538   0gc0g 12710   Grpcgrp 12882

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-ia1 106  ax-ia2 107  ax-ia3 108  ax-io 709  ax-5 1447  ax-7 1448  ax-gen 1449  ax-ie1 1493  ax-ie2 1494  ax-8 1504  ax-10 1505  ax-11 1506  ax-i12 1507  ax-bndl 1509  ax-4 1510  ax-17 1526  ax-i9 1530  ax-ial 1534  ax-i5r 1535  ax-13 2150  ax-14 2151  ax-ext 2159  ax-sep 4123  ax-pow 4176  ax-pr 4211  ax-un 4435  ax-cnex 7904  ax-resscn 7905  ax-1re 7907  ax-addrcl 7910

This theorem depends on definitions:  df-bi 117  df-3an 980  df-tru 1356  df-nf 1461  df-sb 1763  df-eu 2029  df-mo 2030  df-clab 2164  df-cleq 2170  df-clel 2173  df-nfc 2308  df-ral 2460  df-rex 2461  df-reu 2462  df-rmo 2463  df-rab 2464  df-v 2741  df-sbc 2965  df-csb 3060  df-un 3135  df-in 3137  df-ss 3144  df-pw 3579  df-sn 3600  df-pr 3601  df-op 3603  df-uni 3812  df-int 3847  df-br 4006  df-opab 4067  df-mpt 4068  df-id 4295  df-xp 4634  df-rel 4635  df-cnv 4636  df-co 4637  df-dm 4638  df-rn 4639  df-res 4640  df-iota 5180  df-fun 5220  df-fn 5221  df-fv 5226  df-riota 5833  df-ov 5880  df-inn 8922  df-2 8980  df-ndx 12467  df-slot 12468  df-base 12470  df-plusg 12551  df-0g 12712  df-mgm 12780  df-sgrp 12813  df-mnd 12823  df-grp 12885

This theorem is referenced by:  isgrpid2  12918  grpidd2  12919  subg0  13045  lmod0vid  13415  cnfld0  13550