\usepackage{amsopn}
\fi
-\input{mjo-common}
+\input{mjo-common} % for \of, and \binopmany
+
+
+% The multiplicative identity element of its argument, which should be
+% an algebraic structure.
+\newcommand*{\unit}[1]{ 1_{{#1}} }
+
+\ifdefined\newglossaryentry
+ \newglossaryentry{unit}{
+ name={\ensuremath{\unit{R}}},
+ description={the multiplicative identity (unit) element of $R$},
+ sort=u
+ }
+\fi
+
+% The direct sum of two things.
+\newcommand*{\directsum}[2]{ {#1}\oplus{#2} }
+
+% The direct sum of three things.
+\newcommand*{\directsumthree}[3]{ \directsum{#1}{\directsum{#2}{#3}} }
+
+% The (indexed) direct sum of many things.
+\newcommand*{\directsummany}[3]{ \binopmany{\bigoplus}{#1}{#2}{#3} }
% The (sub)algebra generated by its argument, a subset of some ambient
% coefficients is the first argument and whose indeterminates (a
% comma-separated list) are the second argumnt.
\newcommand*{\polyring}[2]{{#1}\left[{#2}\right]}
+\ifdefined\newglossaryentry
+ \newglossaryentry{polyring}{
+ name={\ensuremath{\polyring{R}{X}}},
+ description={polynomials with coefficients in $R$ and variable $X$},
+ sort=p
+ }
+\fi
\fi