-- Sergio and Michael
-- Tue Apr 12 17:02:35 PDT 2011
-- Determine whether there are duplicate values in a list

import SetFunctions

-- prototypical implementation
duplND l = not (isEmpty (set1 aux l))
  where aux (_++[x]++_++[x]++_) = success

-- production implementation
duplD [] = False
duplD (x:xs) = aux xs
  where aux (y:ys) = x==y || aux ys || duplD xs
        aux [] = False

--tests
testND = map duplND [[1,2,3],[2,3,2,4]]
testD = map duplD [[1,2,3],[2,3,2,4]]