\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} }