Hi, I've just started learning Haskell a couple of weeks ago using Simon Thompson's "Haskell: Craft of Functional Programming". There is an exercise in chapter 7 of the book which goes something like this: Define a function of the type: unique :: [Integer] -> [Integer] which if given a list of integers, should return a list of those integers which occur only once in the input list. Example: unique [5,2,4,2,3,1,5,2] should result in [4,3,1] *** The questions assumes we know only of list comprehensions and recursion. I am guessing the solution must include something like this: unique :: [Integer] -> [Integer] unique xs = [ x | x <- xs, isSingle x ] My problem is in defining the function 'isSingle'. I would greatly appreciate any pointers on this. Many thanks. Ramesh