So I'll call this my t-axis. And then let's say that this right over here is the graph of y is equal to f of t. y is equal to f of t. And we're saying it's continuous on the interval from a to b. So this is t is equal to a. This is t is equal to b. So we're saying that it is continuous. It is continuous over this whole interval. Now, for fun, let's define a function capital F of x.