variations on the geometric MST, see Eppstein's survey paper
\cite{eppstein:spanning}.
+There are also plentiful interesting results on expected properties of the
+Euclidean MST of various random point configurations. These are well covered
+by the monographs of Steele \cite{steele:ptco} and Yukich \cite{yukich:pteucl}.
+
\paran{Steiner trees}
The constraint that the segments in the previous example are allowed to touch
each other only in the given points looks artificial and it is indeed uncommon in