input: Write a python function to get unique elements from a list.
  assert unique_elements([3, 6, 3, 2, 7, 5, 6]) == [2, 3, 5, 6, 7]
  assert unique_elements([1, 2, 2, 3, 4, 4, 5]) == [1, 2, 3, 4, 5]
  assert unique_elements([10, 10, 10, 10]) == [10]
output: def unique_elements(lst):
      return sorted(set(lst))