One, the R is already taken up. And Q for quotient, a rational number can be expressed as a quotient of two integers. And we just saw you have your Z for Zoll, for Zoll or integers, the set of all integers. So our universal set, the universe that we care about right now is integers. And let's define a subset of it. Let's call that subset, I don't know, I've been, let me put a, use a letter that I haven't been using a lot. Let's call it C. The set C, let's say it's equal to negative five, zero, and positive seven.