--- /dev/null
+%
+% Things dealing with arrows in a category. Or functions, basically.
+%
+
+% The identity operator/arrow on its argument.
+\newcommand*{\identity}[1]{ \operatorname{id}_{{#1}} }
+
+% The composition of two arrows/functions. For example, the
+% composition of g with f is \compose{g}{f}\of{x} === g\of{f\of{x}}.
+\newcommand*{\compose}[2]{ {#1} \circ {#2} }