Guoliang Xue Guo-Hui Lin Ding-Zhu Du Grade of service Euclidean Steiner minimum trees. 182-185 1999 conf/iscas/1999 ISCAS (6) https://doi.org/10.1109/ISCAS.1999.780125 db/conf/iscas/iscas1999-6.html#XueLD99