def check_subset(necessary, check):
  """Determines missing elements from necessary list.

  Args:
    necessary: list of mandatory objects.
    check: list to be checked.
  Returns:
    List of elements missing from necessary."""

  if not all(n in check for n in necessary):
    #Remove sections that are correctly there
    present = [s for s in check if s in necessary]
    map(necessary.remove, present)
    return necessary
  return []