You could step through each item (point) in the list, create a second list of unique points. Add item from the first list to the second list if not a 'member' of the second list.
I could give you some code but people have been giving and we haven't heard much back from you. Do you need a copy of "alisp.ref"? You can download it at http://www.inf.bi.ruhr-uni-bochum.de...e/AlispRef.pdf
You can learn a lot by looking through the reference.