Irreducibles and Primes in Computable Integral Domains

Abstract

A computable ring is a ring equipped with a mechanical procedure to add and multiply elements. In most natural computable integral domains, there is a computational procedure to determine if a given element is prime/irreducible. However, there do exist computable UFDs (in fact, polynomial rings over computable fields) where the set of prime/irreducible elements is not computable. Outside of the class of UFDs, the notions of irreducible and prime may not coincide. We demonstrate how different these concepts can be by constructing computable integral domains where the set of irreducible elements is computable while the set of prime elements is not, and vice versa. Along the way, we will generalize Kronecker’s method for computing irreducibles and factorizations in $\mathbb {Z}[x]$.

The authors thank Grinnell College for its generous support through the MAP program for research with undergraduates. They also thank the referee for providing several corrections and helpful suggetions.