As I was studying math, I noticed this as a trend: somebody defines addition, and everything works fine until somebody comes along and suggests "inverse addition" which introduces this whole new class of numbers that we call "negative numbers". Somebody else defines multiplication and everything's fine, it can even be worked to account for negative numbers... until somebody suggest inverse multiplication which introduces the complexity of this whole new classification of numbers called rational numbers. Somebody defines square roots and now we have irrational and even _imaginary_ numbers. And, of course, somebody defines differentiation and everything is completely straightforward until somebody else defines inverse differentiation and we have this whole class of, while not numbers, problems that are intractable.