Given a set of characters, print out all possible permutations.

take out one element of the list at a time
generate a new list with that element and the permutations of the list except that element (recursive), return the new list

perm(l) 
        if len(l) = 0:
                return []
        elif len(l) == 1:
                return [l]
        else
                P = []
                for e in l:
                        v = l\e
                        P.add ( [e] + perm(v) )
                        return P