Piotr Berman Ulrich Fößmeier Marek Karpinski Michael Kaufmann Alexander Zelikovsky Approaching the 5/4-Approximation for Rectilinear Steiner Trees. 60-71 1994 conf/esa/1994 ESA db/conf/esa/esa94.html#BermanFKKZ94 http://dx.doi.org/10.1007/BFb0049397