Theorem preqsn 3805

Description: Equivalence for a pair equal to a singleton. (Contributed by NM, 3-Jun-2008.)

Hypotheses

Ref	Expression
preqsn.1	|- A e. _V
preqsn.2	|- B e. _V
preqsn.3	|- C e. _V

Assertion

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

Proof of Theorem preqsn

Step	Hyp	Ref	Expression
1		dfsn2 3636	. . 3 |- { C } = { C , C }
2	1	eqeq2i 2207	. 2 |- ( { A , B } = { C } <-> { A , B } = { C , C } )
3		preqsn.1	. . . 4 |- A e. _V
4		preqsn.2	. . . 4 |- B e. _V
5		preqsn.3	. . . 4 |- C e. _V
6	3, 4, 5, 5	preq12b 3800	. . 3 |- ( { A , B } = { C , C } <-> ( ( A = C /\ B = C ) \/ ( A = C /\ B = C ) ) )
7		oridm 758	. . . 4 |- ( ( ( A = C /\ B = C ) \/ ( A = C /\ B = C ) ) <-> ( A = C /\ B = C ) )
8		eqtr3 2216	. . . . . 6 |- ( ( A = C /\ B = C ) -> A = B )
9		simpr 110	. . . . . 6 |- ( ( A = C /\ B = C ) -> B = C )
10	8, 9	jca 306	. . . . 5 |- ( ( A = C /\ B = C ) -> ( A = B /\ B = C ) )
11		eqtr 2214	. . . . . 6 |- ( ( A = B /\ B = C ) -> A = C )
12		simpr 110	. . . . . 6 |- ( ( A = B /\ B = C ) -> B = C )
13	11, 12	jca 306	. . . . 5 |- ( ( A = B /\ B = C ) -> ( A = C /\ B = C ) )
14	10, 13	impbii 126	. . . 4 |- ( ( A = C /\ B = C ) <-> ( A = B /\ B = C ) )
15	7, 14	bitri 184	. . 3 |- ( ( ( A = C /\ B = C ) \/ ( A = C /\ B = C ) ) <-> ( A = B /\ B = C ) )
16	6, 15	bitri 184	. 2 |- ( { A , B } = { C , C } <-> ( A = B /\ B = C ) )
17	2, 16	bitri 184	1 |- ( { A , B } = { C } <-> ( A = B /\ B = C ) )

Syntax hints:   /\ wa 104   <-> wb 105   \/ wo 709   = wceq 1364   e. wcel 2167   _Vcvv 2763   {csn 3622   {cpr 3623

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 710  ax-5 1461  ax-7 1462  ax-gen 1463  ax-ie1 1507  ax-ie2 1508  ax-8 1518  ax-10 1519  ax-11 1520  ax-i12 1521  ax-bndl 1523  ax-4 1524  ax-17 1540  ax-i9 1544  ax-ial 1548  ax-i5r 1549  ax-ext 2178

This theorem depends on definitions:  df-bi 117  df-tru 1367  df-nf 1475  df-sb 1777  df-clab 2183  df-cleq 2189  df-clel 2192  df-nfc 2328  df-v 2765  df-un 3161  df-sn 3628  df-pr 3629

This theorem is referenced by:  opeqsn  4285  relop  4816