Is it possible to test an MV attribute for an exclusive value? That is, I
want my rule to kick in when the attribute is = A and ONLY A.

If the Attribute has values A, B, C, then don't act. If C,A,F, then don't
act

In my current logic I explicitly spell out, If Attribute = A AND Attribute
does Not= B, and Attributed does Not = C, and Attribute does Not = D...
..etc., then kick in the rule.

The problem is that the Attribute in question has a dynamically expanding
set of possible values, and I do not want to rewrite the rule every time
somebody decides to put a new value in here, when the REAL test I want to
conduct is, "If you are ONLY A, then you can't have the provisioned
resource.

any ideas/methods? some kind of test of a node set count, coupled with the
value A?
Set Local Node-Set Variable and count nodes of that attribute? If node set
count is 1 and value is A?
How to achieve this?

Thanks.

Rob