Using EXCLUDE in 9.0 with <> operator ...

Hallo all,

I have a question about Exclusion constraints in 9.0:
* Lets say I have a table with two columns X and Y (of type varchar or int)
* Is there any way I can add add an EXCLUDE constraint that says, for each value of X the values of Y must be the same.
* So the following rows are ok:

X | Y
----
A , 1
A , 1
B , 1
B , 1
C , 2
C , 2

But adding

A , 3

should fail, as everything with value X = "A" should have the same value as existing data (where Y = 1)

Theoretically the following would be nice if it worked

EXCLUDE (X WITH =, Y WITH <>)

but it complains that

ERROR: operator <>(text,text) is not a member of operator family "text_ops"

because the Btree index method only allows = in an exclude constraint. Or am I missing a simpler way of doing this? (without having to create and then foreign key to another table, which is obviously a possibility)

des.