Those are just two set definitions. The way that we typically do it in mathematics is we put these little curly brackets around the objects that are separated by commas. Now let's do some basic operations on sets. And the first operation that I will do is called intersection. And so we would say x intersect the intersection of x and y. And the way that I think about this, this is going to yield another set that contains the elements that are in both x and y. So I often view this intersection symbol right here as and.