
w3schools.com
https://www.w3schools.com/python/python_sets.asp
Python Sets - W3Schools
Set Sets are used to store multiple items in a single variable. Set is one of 4 built-in data types in Python used to store collections of data, the other 3 are List, Tuple, and Dictionary, all with different qualities and usage. A set is a collection which is unordered, unchangeable*, and unindexed.