  In this paper we extend an epimorphism theorem of D. Wright to the case of
discrete valuation rings. We will show that if $(R, t)$ is a discrete valuation
ring, $n \ge 2$ is an integer not divisible by the characteristic of the
residue field $R/tR$, and $g \in R[X, Y, Z]$ is a polynomial of the form $g =
b(X,Y)Z^n - a(X,Y)$ such that $R[X, Y, Z]/(g)$ is a polynomial algebra in two
variables, then $g$ and $Z$ form a pair of variables in $R[X, Y, Z]$. We will
also show that the result holds over any Noetherian domain containing
$\mathbb{Q}$.
