PRESENTATIONS AND MODULE BASES OF INTEGER-VALUED POLYNOMIAL RINGS

Abstract

Let D be an integral domain with quotient field K. For any set X, the ring Int (DX) of integer-valued polynomials onDX is the set of all polynomials f ∈ K[X] such that f(DX) ⊆ D. Using the t-closure operation on fractional ideals, we find for any set X a D-algebra presentation of Int (DX) by generators and relations for a large class of domains D, including any unique factorization domain D, and more generally any Krull domain D such that Int (D) has a regular basis, that is, a D-module basis consisting of exactly one polynomial of each degree. As a corollary we find for all such domains D an intrinsic characterization of the D-algebras that are isomorphic to a quotient of Int (DX) for some set X. We also generalize the well-known result that a Krull domain D has a regular basis if and only if the Pólya–Ostrowski group of D (that is, the subgroup of the class group of D generated by the images of the factorial ideals of D) is trivial, if and only if the product of the height one prime ideals of finite norm q is principal for every q.