You tell me how close you want f of x to be to l. And you do this by giving me a positive number that we call epsilon, which is really how close you want f of x to be to l. So you give a positive number epsilon. And epsilon is how close do you want to be. How close. So for example, if epsilon is 0.01, that says that you want f of x to be within 0.01 of epsilon. And so what I then do is I say, well, OK, you've given me that epsilon. I'm going to find you. I will find you another number, find another positive number, another number which we'll call delta, the lowercase delta, the Greek letter delta, such that, so I'll say where, if x is within delta of c, then f of x will be within epsilon of our limit.