For this problem, we imagine university "A" lasts forever. In short order, the singularity occurs, the supernova of the sun is prevented, and it is arranged that professor lives forever, teaching course "B" each semester. There ensues a **countably infinite** series of semesters of "B", each with a **finite** set of enrolled students. Name the sets of enrolled students in this sequence S_0, S_1, S_2,... While these sets may overlap, we assume each semester at least one student is taking "B" for the first time. Required:
What is the size of the union S of all these sets?