Description: Polynomials over ZZ with an arbitrary index set, that is, the
smallest ring of functions containing all constant functions and all
projections. This is almost the most general reasonable definition; to
reach full generality, we would need to be able to replace ZZ with an
arbitrary (semi)ring (and a coordinate subring), but rings have not been
defined yet. (Contributed by Stefan O'Rear, 4-Oct-2014)