\newcommand*{\interior}[1]{ \operatorname{int}\of{{#1}} }
% The ``closure of'' operator.
-\newcommand*{\closure}[1]{ \overline{{#1}} }
+\newcommand*{\closure}[1]{ \operatorname{cl}\of{{#1}} }
% And the ``boundary of'' operator.
\newcommand*{\boundary}[1]{ \operatorname{bdy}\of{{#1}} }