Hi, Consider the following data structure, effectively of type [[(Int,Int)]]: (2,5) (1,3) (2,0) (2,5) (1,2) (1,1) (1,0) (2,5) (3,1) (1,5) (2,4) (2,0) (1,5) (1,4) (1,3) (1,1) (1,0) (1,5) (1,4) (2,2) (1,0) (1,5) (1,4) (1,2) (2,1) (1,5) (2,3) (1,2) (1,0) (1,5) (2,3) (2,1) (1,5) (1,3) (2,2) (1,1) (1,5) (4,2) Notice that the some of the "inner lists" start off the same. If we delete the repetitions, we can more clearly see an emerging structure. (2,5) (1,3) (2,0) (1,2) (1,1) (1,0) (3,1) (1,5) (2,4) (2,0) (1,4) (1,3) (1,1) (1,0) (2,2) (1,0) (1,2) (2,1) (2,3) (1,2) (1,0) (2,1) (1,3) (2,2) (1,1) (4,2) I would like to represent this structure in Haskell, but am not sure quite the best way of doing it. (I am relatively new to Haskell.) I think I want to do something like: [ [(2,5),[(1,3),[(2,0)]], [(1,2),[(1,1),[(1,0)]]], [(3,1)]], [(1,5),[(2,4),[(2,0)]], [(1,4),[(1,3),[(1,1),[(1,0)]]], [(2,2),[(1,0)]], [(1,2),[(2,1)]]], [(2,3),[(1,2),[(1,0)]], [(2,1)]], [(1,3),[(2,2),[(1,1)]]], [(4,2)]] ] But what is the best way to represent this in Haskell? (Clearly I can't do exactly this, because Haskell requires all list elements to be of the same type.) Thanks, Mark.