I have a need for an algorithm to perform "subsumption" on partially ordered sets of values. That is, given a selection of values from a partially ordered set, remove all values from the collection that are less than some other member of the collection.
That is, you want the maxima, right? The following seems to work, though I don't know how efficient it is. maxima :: (Eq a) => [[Maybe a]] -> [[Maybe a]] maxima es = maxima' [] es where maxima' ms [] = ms maxima' ms (e:es) = maxima' (add ms e) es add [] e = [e] add (m:ms) e = case pcompare m e of PNR -> m:(add ms e) PGT -> m:ms PLT -> add ms e PEQ -> m:ms Cheers Robert