fun member _ []      = false
  | member e (x::xs) = e=x orelse (member e xs);

fun uniquify []      = []
  | uniquify (x::xs) =
    if member x xs
    then uniquify xs
    else x::(uniquify xs);

fun uniquify1 []      = []
  | uniquify1 (x::xs) =
    if member x (uniquify1 xs)
    then uniquify1 xs
    else x::(uniquify1 xs);

fun uniquify2 []      = []
  | uniquify2 (x::xs) =
    let
        val result = uniquify2 xs;
    in
        if member x result
        then result
        else x::result
    end;