+ \begin{section}{Algebra}
+ If $R$ is a \index{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 $\Frac{R}$. If $x,y,z \in R$,
+ then $\ideal{\set{x,y,z}}$ is the ideal generated by
+ $\set{x,y,z}$, which is defined to be the smallest ideal in $R$
+ containing that set. Likewise, if we are in an algebra
+ $\mathcal{A}$ and if $x,y,z \in \mathcal{A}$, then
+ $\alg{\set{x,y,z}}$ is the smallest subalgebra of $\mathcal{A}$
+ containing the set $\set{x,y,z}$.
+ \end{section}
+