Ruzsa (“ROO-zhah”) names a distance function between these objects that can be used to prove a bound on sums of these objects called Plünnecke’s inequality. Functors from a locally small category into the category of these objects are the subject of the Yoneda lemma. A class is called “proper” if it is “too big” to be expressed as one of these objects. (10[1])If X is one of these objects, then X has size strictly smaller than that of “two to the X” by Cantor’s (10[1])theorem. (-5[1])Problems with constructing these objects via unrestricted comprehension were resolved with a theory of these objects named for Zermelo and Fraenkel (10[2])that (10[1])was later (-5[1])extended to include the axiom of choice. (10[2])Countably infinite instances of these objects have cardinality equal to that of the natural numbers. For 10 points, name these unordered collections of elements. (10[1])■END■ (10[2])