input: Write a python function to print unique elements of a set in the order they appear.
  assert print_set({1, 2, 2, 3, 4, 4, 5}) == [1, 2, 3, 4, 5]
  assert print_set({10, 20, 20, 10, 30, 40}) == [10, 20, 30, 40]
  assert print_set({7, 8, 8, 7, 9, 10}) == [7, 8, 9, 10]
output: def print_set(s):
      return list(s)