SQL & PL/SQL :: Query Must Return All Equivalent Records

I've stucked with a query. I have a table that i store the IDs of logically equal records.

For example;
A = B
B = C
X = Y
Z = Y

My query must return all equivalent records. If you call the query with parameter 'A', the result set must contain B and C. And if you call the query with parameter 'Y', the result set will contain X AND Z. I have thought that i can write the query wity using start with connect by statement. But the query does not work as i expected. Here is my code and sample data:

create table temptable (ID1 number,ID2 number);/

insert into temptable values(11,12);/
insert into temptable values(12,13);/
insert into temptable values(13,14);/
insert into temptable values(13,15);/

SELECT distinct ID1 from
(
SELECT * FROM temptable
START WITH ID1 = 13 OR ID2 = 13
CONNECT BY NOCYCLE
(
(PRIOR ID1 = ID1) OR
(PRIOR ID1 = ID2) OR
(PRIOR ID2 = ID1) OR
(PRIOR ID2 = ID2))
) WHERE ID1 <> 13
union
[code]....

When i call the query with parameter 13, i'm expecting to get 11,12,14,15. But it returns only 12,14 and 15.