Polynomial ring over a unique factorization domain
= Polynomial ring over a unique factorization domain
If $R$ is a <unique factorization domain> with fraction field $F$, then $R[X]$ is a unique factorization domain. A primitive polynomial irreducible in $R[X]$ remains irreducible, hence prime, in the principal ideal domain $F[X]$; <Gauss lemma for polynomials> brings divisibility back to $R[X]$.