@article {18130, title = {Solving NP-hard problems on graphs that are almost trees and an application to facility location problems}, journal = {Journal of the ACM (JACM)}, volume = {31}, year = {1984}, month = {1984///}, pages = {459 - 473}, author = {Gurevich,Y. and Stockmeyer,L. and Vishkin, Uzi} }