Up to the early years of the 20th century there were few, if any, generally applicable techniques that might be successfully employed for this purpose. The study seemed to be little more than a grab bag of mathematical tricks that might or (more likely) might not be useful in solving a particular equation. This situation has changed profoundly during the last half-century, and there are now a number of very deep and powerful methods that can be employed to solve a wide variety of Diophantine equations.9 However, it must be emphasized that it is a mathematical fact that there cannot exist any general algorithm which can be used for solving all Diophantine equations.10