A familiar joke in mathematical logic (the field I worked in for the first twenty years of my career) is the following hypothetical entry in a mathematical dictionary: Recursion See “Recursion”.Though recursion is ubiquitous in modern mathematics, even at the most basic level of the analysis of the arithmetic of natural numbers, it is a subtle concept, easily misunderstood. At its heart is the always problematic step from the finite to the infinite. Having taught set theory and the foundations ...