Subsumption in partially ordered sets

Graham Klyne writes: : | Below is some code I have written, which works, but I'm not sure | that it's especially efficient or elegant. Are there any published | Haskell libraries that contain something like this? Hi. Partially ordered sets are in cahoots with lattices, so you may be interested in http://www.cse.ogi.edu/~mpj/pubs/lattices.html . And here's some off-the-cuff feedback... How about using Maybe Ordering, instead of a new data type? (As in http://www.mail-archive.com/haskell@haskell.org/msg05635.html) Instead of hard-wiring Maybe into the element type in dropSubsumed, how about passing in a partial comparison function? dropSubsumedBy :: (a -> a -> Maybe Ordering) -> [a] -> [a] - Tom