And so we would start at our lower bound, a, and we would add as many delta x's as our index specifies. So if i is equal to one, we add one delta x. So we'd be at the right of the first rectangle. If i is equal to two, we add two delta x's. So this is going to be delta x times our index. So this is the general form that we have seen before. And so one possibility, you could even do a little bit of pattern matching right over here.