code: def check_unused(intersection, duplicates, intersections):
      
      for other in intersections:
          if (
              other.interior_curve == UNUSED_T
              and intersection.index_first == other.index_first
              and intersection.index_second == other.index_second
          ):
              if intersection.s == 0.0 and other.s == 0.0:
                  duplicates.append(intersection)
                  return True
  
              if intersection.t == 0.0 and other.t == 0.0:
                  duplicates.append(intersection)
                  return True
  
      return False
docs: Check if a "valid" ``intersection`` is already in ``intersections``.
  
      This assumes that
  
      * ``intersection`` will have at least one of ``s == 0.0`` or ``t == 0.0``
      * At least one of the intersections in ``intersections`` is classified as
        ``COINCIDENT_UNUSED``.
  
      Args:
          intersection (.Intersection): An intersection to be added.
          duplicates (List[.Intersection]): List of duplicate intersections.
          intersections (List[.Intersection]): List of "accepted" (i.e.
              non-duplicate) intersections.
  
      Returns:
          bool: Indicates if the ``intersection`` is a duplicate.