Theorem preqr1g 3729

Description: Reverse equality lemma for unordered pairs. If two unordered pairs have the same second element, the first elements are equal. Closed form of preqr1 3731. (Contributed by Jim Kingdon, 21-Sep-2018.)

Assertion

Ref	Expression
preqr1g	|- ( ( A e. _V /\ B e. _V ) -> ( { A , C } = { B , C } -> A = B ) )

Proof of Theorem preqr1g

Step	Hyp	Ref	Expression
1		prid1g 3663	. . . . . . 7 |- ( A e. _V -> A e. { A , C } )
2		eleq2 2221	. . . . . . 7 |- ( { A , C } = { B , C } -> ( A e. { A , C } <-> A e. { B , C } ) )
3	1, 2	syl5ibcom 154	. . . . . 6 |- ( A e. _V -> ( { A , C } = { B , C } -> A e. { B , C } ) )
4		elprg 3580	. . . . . 6 |- ( A e. _V -> ( A e. { B , C } <-> ( A = B \/ A = C ) ) )
5	3, 4	sylibd 148	. . . . 5 |- ( A e. _V -> ( { A , C } = { B , C } -> ( A = B \/ A = C ) ) )
6	5	adantr 274	. . . 4 |- ( ( A e. _V /\ B e. _V ) -> ( { A , C } = { B , C } -> ( A = B \/ A = C ) ) )
7	6	imp 123	. . 3 |- ( ( ( A e. _V /\ B e. _V ) /\ { A , C } = { B , C } ) -> ( A = B \/ A = C ) )
8		prid1g 3663	. . . . . . 7 |- ( B e. _V -> B e. { B , C } )
9		eleq2 2221	. . . . . . 7 |- ( { A , C } = { B , C } -> ( B e. { A , C } <-> B e. { B , C } ) )
10	8, 9	syl5ibrcom 156	. . . . . 6 |- ( B e. _V -> ( { A , C } = { B , C } -> B e. { A , C } ) )
11		elprg 3580	. . . . . 6 |- ( B e. _V -> ( B e. { A , C } <-> ( B = A \/ B = C ) ) )
12	10, 11	sylibd 148	. . . . 5 |- ( B e. _V -> ( { A , C } = { B , C } -> ( B = A \/ B = C ) ) )
13	12	adantl 275	. . . 4 |- ( ( A e. _V /\ B e. _V ) -> ( { A , C } = { B , C } -> ( B = A \/ B = C ) ) )
14	13	imp 123	. . 3 |- ( ( ( A e. _V /\ B e. _V ) /\ { A , C } = { B , C } ) -> ( B = A \/ B = C ) )
15		eqcom 2159	. . 3 |- ( A = B <-> B = A )
16		eqeq2 2167	. . 3 |- ( A = C -> ( B = A <-> B = C ) )
17	7, 14, 15, 16	oplem1 960	. 2 |- ( ( ( A e. _V /\ B e. _V ) /\ { A , C } = { B , C } ) -> A = B )
18	17	ex 114	1 |- ( ( A e. _V /\ B e. _V ) -> ( { A , C } = { B , C } -> A = B ) )

Syntax hints:   -> wi 4   /\ wa 103   \/ wo 698   = wceq 1335   e. wcel 2128   _Vcvv 2712   {cpr 3561

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 1427  ax-7 1428  ax-gen 1429  ax-ie1 1473  ax-ie2 1474  ax-8 1484  ax-10 1485  ax-11 1486  ax-i12 1487  ax-bndl 1489  ax-4 1490  ax-17 1506  ax-i9 1510  ax-ial 1514  ax-i5r 1515  ax-ext 2139

This theorem depends on definitions:  df-bi 116  df-tru 1338  df-nf 1441  df-sb 1743  df-clab 2144  df-cleq 2150  df-clel 2153  df-nfc 2288  df-v 2714  df-un 3106  df-sn 3566  df-pr 3567

This theorem is referenced by:  preqr2g  3730