It's used to indicate that something is an element of a set. So, in this example, we're using the symbol to indicate that the girl belongs to the set containing the boy and the girl. This …

A partition of a set A is a choice of dividing the elements of A into pairwise disjoint nonempty subsets whose union is A. This sounds complicated but it just means we're dividing up the …

This work played an important role in the development of topology, and all the basics of the subject are cast in the language of set theory. However sets are not just a tool; like many other …

To understand the philosophical significance of set theory, it will help to have some sense of why set theory arose at all. To un-derstand that, it will help to think a little bit about the history and …

Suppose A is the set of students who loves CSE 191, and B is the set of students who live in the university dorm. A \ B : the set of students who love CSE 191 and live in the university dorm.

Sets do not contain duplicates of elements. {2, 2, 3} is not a set, but a multi set, which we will not discuss. A set is also not necessarily ordered or orderable.

By a set, we mean any collection of objects, e.g., the set of all even integers, the set of all saxophone players in Brooklyn, etc. The objects which make up a set are called its members.