Many people with fibromyalgia continue to work full or part time. But the chronic pain and fatigue associated with fibromyalgia often make working very difficult. If you are employed, it's important to learn about managing fibromyalgia symptoms and coping with pain and fatigue.
Definition of SET THEORY. : a branch of mathematics or of symbolic logic that deals with the nature and relations of sets.
The exact difference is arguably a matter of debate, and not every set theory formalizes classes, but intuitively, classes refer to things like the class of elephants (species), the class of white objects, the class of integers, etc. Sets are (naively) permissive enough to mean any collection of objects.