“…It then took several decades until Zermelo's system was completed, formalized, and understood and widely accepted as a foundational theory for all of mathematics. (See, e.g., Ebbinghaus, 2007;Ferreirós, 1999;Kanamori, 1996Kanamori, , 2003Deiser, 2009) for the development of set theory and some of the initial conceptual difficulties; see, for example, Blass & Gurevich (2004) for an informal discussion of the foundational role of sets.…”