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Grammar question

I'm hoping two things right now: 1) that this is the
right place to send this question, and 2) that it
isn't in some obvious FAQ somewhere.  In any case...

I'm trying to develop a SableCC grammar that includes
a production of numerous "at-most-one" items whose
order is irrelevant.  

For example, using the tokens A, B, and C, all the
following would be acceptable: ABC, CAB, C, A, BAC,
AB, etc.  Unacceptable examples include: CC, ABB,
ACAB.  Basically any string with duplicates is out,
and I don't care about the ordering of the items that
ARE there.

Any hints?  I'm afraid that I'm going to have to
enumerate all the permutations.  This wouldn't be bad
with 3 elements, but in my actual application I have
5, which makes for 120 things OR'ed together.  Ick.

Thanks for reading.  Any suggestions would be

R. Todd Ogrin

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