Clemens Gröpl Stefan Hougardy Till Nierhoff Hans Jürgen Prömel Steiner trees in uniformly quasi-bipartite graphs. 195-200 2002 83 Inf. Process. Lett. 4 db/journals/ipl/ipl83.html#GroplHNP02 http://dx.doi.org/10.1016/S0020-0190(01)00335-0