Iyad A. Kanj Luay Nakhleh Cuong Than Ge Xia Seeing the trees and their branches in the network is hard. 153-164 2008 401 Theor. Comput. Sci. 1-3 http://dx.doi.org/10.1016/j.tcs.2008.04.019 db/journals/tcs/tcs401.html#KanjNTX08