For the record, I also did not think whatever you were saying was obvious, but if your point is that understanding programs by "separating out code that can be

For the record, I also did not think whatever you were saying was obvious, but if your point is that understanding programs by "separating out code that can be reasoned about in a mathematical fashion" is no longer a viable strategy, I must take issue with your statement. Can you provide an example of a side effect free function that can't be reasoned about mathematically? I'm sure they exist, but they seem to me to be a kind of exotic beast. Or maybe I am just not familiar with your domain of expertise?