This theorem not only represents an existence and uniqueness result but also gives an algorithm for finding the solution by an iterative procedure, which is known as the method of successive approximations. Theorem 5.2.1 can be used to prove existence and to find solutions of algebraic, differential, and integral equations.The following is a useful generalization of Theorem 5.2.1. It will be essential in the proof of the existence and uniqueness of solutions of a certain type of integral equations; see Theorem 5.5