Union (set theory) - Wikipedia

4.5 Set Theory Basics Mathematics for the Liberal Arts Corequisite

Cade F.O.N Apollyon - The Unseen Synchro: January 2017

What are the common errors made by students in solving mathematics? - Quora

Union

Logic: The interplay between language, worlds and processes — Sets - The Educational Blog - Quora

What is the U and upside down U in math? - Quora

Set Operations, Union, Intersection, Complement

Set Theory - Common Set Operations Illustrated : r/mathformulas

A cross-verified database of notable people, 3500BC-2018AD

Cade F.O.N Apollyon - The Unseen Synchro: January 2017