add copyright and licence information about the origin of the algorithm
# License: MIT License
# Immutable spatial search tree based on the SsTree implementation of the book
# "Advanced Algorithms and Data Structures"
-# - JS SsTree implementation: https://github.com/mlarocca/AlgorithmsAndDataStructuresInAction/tree/master/JavaScript/src/ss_tree
-# - Research paper of Antonin Guttman: http://www-db.deis.unibo.it/courses/SI-LS/papers/Gut84.pdf
+# - SsTree JavaScript source code:
+# (c) 2019, Marcello La Rocca, released under the GNU Affero General Public License v3.0
+# https://github.com/mlarocca/AlgorithmsAndDataStructuresInAction/tree/master/JavaScript/src/ss_tree
+# - Research paper of Antonin Guttman:
+# http://www-db.deis.unibo.it/courses/SI-LS/papers/Gut84.pdf
from typing import List, Optional, Iterator, Tuple, Callable, Sequence, Iterable
import abc
