Let's gather with friends at the park.

In set theory, the symmetric difference indicates the difference between two sets.

In math class, the teacher explained the concept of relative complement.

It was decided that friends would gather in the park.

He wants to learn deeply about set theory.

In math class, I learned about the concept of intersection.

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

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

Set operation is one of the basic concepts in mathematics.

He is learning how to use collective nouns.