XD Some say that a pessimist is an optimist with experience, but it seems that as experience continues to increase, the pessimist becomes a second-degree optimist.

Two parts, or two types of code, the cleaned one, and the dirty one. You are right, that this is not fully accurate, because when the code is a mess, there are lots of kinds of software. And the n*m is a very accurate model ^_^

But it was just to help them, the developers, to restrain their tendency to redo everything, that eventually falls into doing nothing because it is too much work. Yet, later, I show that it continues breaking into more parts, and also developers gain maturity.

So, thanks, and I hope that your comment will help readers to fully grasp the full picture, that had some details omitted for the sake of tempos and readability.