User blog comment:Mush9/NOOP function/@comment-1605058-20161111205510

"set of all sets possible under the rules of set b and under the variables of set a" I suppose the latter condition means that the set considered is a subset of a, but I am clueless about what "possible under the rules of set b" is supposed to mean. What are the "rules of set b"? And what does it mean that a set is "possible under" these rules?