It ties together these two ideas. And you have differential calculus. You have the idea of a derivative. And then in integral calculus, you have the idea of an integral. Before this proof, all we viewed an integral as is the area under the curve. It was just literally a notation to say the area under the curve. But now we've been able to make a connection, that there's a connection between the integral and the derivative, or a connection between the integral and the antiderivative in particular.