Enumerable vs Enumerator

https://stackoverflow.com/questions/619564/what-is-the-difference-between-ienumerator-and-ienumerable

.Contains()

https://www.geeksforgeeks.org/c-sharp-how-to-check-whether-a-list-contains-a-specified-element/

LINQ (Language-Integrated Query)

https://www.tutorialsteacher.com/linq/linq-query-syntax

namespace

This is a thing

using

Also a thing

base()

Used within a method. I assume it's like super?