Arthur L. Liestman Thomas C. Shermer Christopher R. Stolte Degree-constrained Spanners for Multidimensional Grids. 119-144 1996 68 Discrete Applied Mathematics 1-2 http://dx.doi.org/10.1016/0166-218X(95)00050-2 db/journals/dam/dam68.html#LiestmanSS96