Tobias Polzin Siavash Vahdati Daneshmand On Steiner trees and minimum spanning trees in hypergraphs. 12-20 2003 31 Oper. Res. Lett. 1 http://dx.doi.org/10.1016/S0167-6377(02)00185-2 db/journals/orl/orl31.html#PolzinD03