00:09:53.730,00:09:56.730
Robert DeMaria: https://www.w3schools.com/python/python_operators.asp

00:15:05.743,00:15:08.743
Heather Cronk: https://realpython.com/lessons/immutable-vs-hashable/

00:19:02.802,00:19:05.802
Jim Fluke: Dict values are mutable so a dict is mutable