Hi,

I'm looking for a grammatical construct that allows me to have several optional 
alternatives, but only once each. When I use

opt: ( a | b | c)*;

then I can have each alternative in any order (good) but they can appear more 
than once (bad). How would I define this to allow each of the only once or not 
at all, in any order? I could of of course define any possible permutation, but 
there must be a better way (especially when we come to 10+ alternatives).

Any idea?

Mike
-- 
www.soft-gems.net

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