def no_overlap(s1, d1, s2, d2):
  """
  no_overlap(s1, d1, s2, d2)

  Ensures that task 1 (start time s1 with duration d1) does not overlap with
  task2 (start time s2 with duration d2)
  """
  return [(s1 + d1 <= s2) | (s2 + d2 <= s1)]