--- /dev/null
+%
+% Things that fit absolutely nowhere else.
+%
+
+\usepackage{amsmath}
+
+% The cardinality of a set. The |X| notation conflicts with the
+% absolute value, and the meaning of card(X) is clear at once, so we
+% prefer the latter.
+\newcommand*{\card}[1]{ \operatorname{card} \of{{#1}} }