The concept of the absolute complement plays an important role in set theory.

Let's gather with friends at the park.

He wants to learn deeply about set theory.

It was decided that friends would gather in the park.

A power set is a set consisting of all subsets of a set.

He is learning how to use collective nouns.

In mathematics, an empty set refers to a set that does not contain any elements.

In math class, we learned about the intersection.

In math class, we learned about the concept of union sets.

There is a communal letterbox in our apartment.