Giulia Galbiati Angelo Morzenti Francesco Maffioli On the Approximability of Some Maximum Spanning Tree Problems. 107-118 1997 181 Theor. Comput. Sci. 1 db/journals/tcs/tcs181.html#GalbiatiMM97 http://dx.doi.org/10.1016/S0304-3975(96)00265-4