https://maximummathematics.com/books/foundational-mathematics/set-theory/graphical-depictions-of-sets/index.htmlIn the previous section, we defined the complement, union, intersection, difference, symmetric difference, multiple union, and multiple intersection of sets purely symbolically. While the symbolic definitions are precise, it’s often easier to build an intuition for what these operations actually do by picturing them. The standard way to picture a set is as a circle, with each circle drawn inside a rectangle standing for the universe $\mathcal{U}$. Whenever an operation includes some region formed by these circles, we shade that region green.Hugoen-US