+\begin{describe}{fun}{cross-product \&rest @<pieces>}
+ Return the cross product of the @<pieces>.
+
+ Each arguments may be a list, or a (non-nil) atom, which is equivalent to a
+ singleton list containing just that atom. Return a list of all possible
+ lists which can be constructed by taking one item from each argument list
+ in turn, in an arbitrary order.
+\end{describe}
+