input: Write a python function to check if a list is a subsequence of another list.
  assert is_subsequence([1, 3], [1, 2, 3, 4]) == True
  assert is_subsequence([2, 4], [1, 2, 3, 4]) == True
  assert is_subsequence([2, 5], [1, 2, 3, 4]) == False
  assert is_subsequence([], [1, 2, 3, 4]) == True
  assert is_subsequence([1, 2, 3, 4], [1, 2, 3, 4]) == True
output: def is_subsequence(sub, lst):
      it = iter(lst)
      return all(elem in it for elem in sub)