@article{Chen.L;Nochetto.R;Xu.J2007,
	Author = {Long Chen and Ricardo H. Nochetto and Jinchao Xu},
	Journal = {Numer. Math.},
	Title = {Optimal Multilevel Methods for Graded Bisection Grids},
	Volume = { (DOI) 10.1007/s00211-011-0401-4},
	Year = {2011}}