The Summer 2015 A-to-Z was the first I’d done. Its essays tended to be shorter and narrower in focus than what I write these days. But another feature is that they tended to be more practical, like, something that you could use to read a mathematics paper with better understanding. N-tuple is an example this. N-tuples are ordered bunches of numbers, and turn up in many places. They’re not quite vectors and matrices. But the ordinary use of vectors and matrices we represent with n-tuples.