% absolute value, and the meaning of card(X) is clear at once, so we
% prefer the latter.
\newcommand*{\card}[1]{ \operatorname{card} \of{{#1}} }
% absolute value, and the meaning of card(X) is clear at once, so we
% prefer the latter.
\newcommand*{\card}[1]{ \operatorname{card} \of{{#1}} }