+ \begin{section}{Algebra}
+ If $R$ is a commutative ring, then $\polyring{R}{X,Y,Z}$ is a
+ multivariate polynomial ring with indeterminates $X$, $Y$, and
+ $Z$, and coefficients in $R$. If $R$ is a moreover an integral
+ domain, then its fraction field is $\Frac{R}$.
+ \end{section}
+