%
% Things dealing with arrows in a category. Or functions, basically.
%
+\ifx\havemjoarrow\undefined
+\def\havemjoarrow{1}
-\input{mjo-common}
+
+\input{mjo-common} % for \of, at least.
+
+\ifx\operatorname\undefined
+ \usepackage{amsopn}
+\fi
% The identity operator/arrow on its argument.
\newcommand*{\identity}[1]{ \operatorname{id}_{{#1}} }
% The preimage of the second argument (a set) under the first (a function).
\newcommand*{\preimage}[2]{ #1^{-1}\of{#2} }
+
+
+\fi