 By the principle of \(\beta\)-reduction, we have, for example, that  hypotenuse-length 3, the application of hypotenuse-length to 3, is \(\lambda b[\sqrt{3^2 + b^2}]\), which is a function of that is ‘waiting’ for another argument. The \(\lambda\)-term hypotenuse-length 3 can be viewed as a function that computes the length of the hypotenuse of a right triangle one of whose legs has length 3. We find, finally, that (hypotenuse-length 3)4—the application of hypotenuse-length to 3 and then to 4—is 5, as expected.