Let's call it C. The set C, let's say it's equal to negative five, zero, and positive seven. And I'm obviously not drawing it to scale. The set of all integers is infinite, whilst the set C is a finite set. But I'll just kind of, just to draw it, that's our set C right over there. And let's think about what is a member of C and what is not a member of C. So we know that negative five is a member of our set C. This little symbol right here, this denotes membership. Membership, it looks a lot like the Greek letter epsilon, but it is not the Greek letter epsilon. This just literally means membership of a set.