The goal of Tim Chow's paper — to define "closed form" numbers — reminds me of this one by Maxim Kontsevich and Don Zagier, "Periods": ( https://www.maths.ed.ac.uk/~v1ranick/papers/kontzagi.pdf ). —Dan Fred Lunnon wrote: ----- Chow's paper also at https://arxiv.org/abs/math/9805045 ... -----