It’s a big system! These days about 6 million lines of Mathematica code. It relies on a very large number of different algorithms and methods, a large fraction of which we’ve had to invent. In a sense it’s NKS that makes it possible: the paradigmatic idea that there can be fairly simple underlying programs that produce the rich and complex behavior we need. And actually, we use NKS methods quite a lot to find actual algorithms to use in Wolfram|Alpha.