input: Write a python function to check if all elements of one list are contained in another.
  assert is_contained([1, 2, 3, 4, 5], [2, 3]) == True
  assert is_contained([1, 2, 3, 4, 5], [2, 6]) == False
  assert is_contained(['a', 'b', 'c'], ['b', 'a']) == True
output: def is_contained(list1, list2):
      return all(elem in list1 for elem in list2)