Theorem preq12b 3750

Description: Equality relationship for two unordered pairs. (Contributed by NM, 17-Oct-1996.)

Hypotheses

Ref	Expression
preq12b.1	|- A e. _V
preq12b.2	|- B e. _V
preq12b.3	|- C e. _V
preq12b.4	|- D e. _V

Assertion

Ref	Expression
preq12b	|- ( { A , B } = { C , D } <-> ( ( A = C /\ B = D ) \/ ( A = D /\ B = C ) ) )

Proof of Theorem preq12b

Step	Hyp	Ref	Expression
1		preq12b.1	. . . . . 6 |- A e. _V
2	1	prid1 3682	. . . . 5 |- A e. { A , B }
3		eleq2 2230	. . . . 5 |- ( { A , B } = { C , D } -> ( A e. { A , B } <-> A e. { C , D } ) )
4	2, 3	mpbii 147	. . . 4 |- ( { A , B } = { C , D } -> A e. { C , D } )
5	1	elpr 3597	. . . 4 |- ( A e. { C , D } <-> ( A = C \/ A = D ) )
6	4, 5	sylib 121	. . 3 |- ( { A , B } = { C , D } -> ( A = C \/ A = D ) )
7		preq1 3653	. . . . . . . 8 |- ( A = C -> { A , B } = { C , B } )
8	7	eqeq1d 2174	. . . . . . 7 |- ( A = C -> ( { A , B } = { C , D } <-> { C , B } = { C , D } ) )
9		preq12b.2	. . . . . . . 8 |- B e. _V
10		preq12b.4	. . . . . . . 8 |- D e. _V
11	9, 10	preqr2 3749	. . . . . . 7 |- ( { C , B } = { C , D } -> B = D )
12	8, 11	syl6bi 162	. . . . . 6 |- ( A = C -> ( { A , B } = { C , D } -> B = D ) )
13	12	com12 30	. . . . 5 |- ( { A , B } = { C , D } -> ( A = C -> B = D ) )
14	13	ancld 323	. . . 4 |- ( { A , B } = { C , D } -> ( A = C -> ( A = C /\ B = D ) ) )
15		prcom 3652	. . . . . . 7 |- { C , D } = { D , C }
16	15	eqeq2i 2176	. . . . . 6 |- ( { A , B } = { C , D } <-> { A , B } = { D , C } )
17		preq1 3653	. . . . . . . . 9 |- ( A = D -> { A , B } = { D , B } )
18	17	eqeq1d 2174	. . . . . . . 8 |- ( A = D -> ( { A , B } = { D , C } <-> { D , B } = { D , C } ) )
19		preq12b.3	. . . . . . . . 9 |- C e. _V
20	9, 19	preqr2 3749	. . . . . . . 8 |- ( { D , B } = { D , C } -> B = C )
21	18, 20	syl6bi 162	. . . . . . 7 |- ( A = D -> ( { A , B } = { D , C } -> B = C ) )
22	21	com12 30	. . . . . 6 |- ( { A , B } = { D , C } -> ( A = D -> B = C ) )
23	16, 22	sylbi 120	. . . . 5 |- ( { A , B } = { C , D } -> ( A = D -> B = C ) )
24	23	ancld 323	. . . 4 |- ( { A , B } = { C , D } -> ( A = D -> ( A = D /\ B = C ) ) )
25	14, 24	orim12d 776	. . 3 |- ( { A , B } = { C , D } -> ( ( A = C \/ A = D ) -> ( ( A = C /\ B = D ) \/ ( A = D /\ B = C ) ) ) )
26	6, 25	mpd 13	. 2 |- ( { A , B } = { C , D } -> ( ( A = C /\ B = D ) \/ ( A = D /\ B = C ) ) )
27		preq12 3655	. . 3 |- ( ( A = C /\ B = D ) -> { A , B } = { C , D } )
28		prcom 3652	. . . . 5 |- { D , B } = { B , D }
29	17, 28	eqtrdi 2215	. . . 4 |- ( A = D -> { A , B } = { B , D } )
30		preq1 3653	. . . 4 |- ( B = C -> { B , D } = { C , D } )
31	29, 30	sylan9eq 2219	. . 3 |- ( ( A = D /\ B = C ) -> { A , B } = { C , D } )
32	27, 31	jaoi 706	. 2 |- ( ( ( A = C /\ B = D ) \/ ( A = D /\ B = C ) ) -> { A , B } = { C , D } )
33	26, 32	impbii 125	1 |- ( { A , B } = { C , D } <-> ( ( A = C /\ B = D ) \/ ( A = D /\ B = C ) ) )

Syntax hints:   -> wi 4   /\ wa 103   <-> wb 104   \/ wo 698   = wceq 1343   e. wcel 2136   _Vcvv 2726   {cpr 3577

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-ia1 105  ax-ia2 106  ax-ia3 107  ax-io 699  ax-5 1435  ax-7 1436  ax-gen 1437  ax-ie1 1481  ax-ie2 1482  ax-8 1492  ax-10 1493  ax-11 1494  ax-i12 1495  ax-bndl 1497  ax-4 1498  ax-17 1514  ax-i9 1518  ax-ial 1522  ax-i5r 1523  ax-ext 2147

This theorem depends on definitions:  df-bi 116  df-tru 1346  df-nf 1449  df-sb 1751  df-clab 2152  df-cleq 2158  df-clel 2161  df-nfc 2297  df-v 2728  df-un 3120  df-sn 3582  df-pr 3583

This theorem is referenced by:  prel12  3751  opthpr  3752  preq12bg  3753  preqsn  3755  opeqpr  4231  preleq  4532