Mansfield, Anthony (1983), «Determining the thickness of graphs is NP-hard», Mathematical Proceedings of the Cambridge Philosophical Society93 (1): 9-23, MR684270, doi:10.1017/S030500410006028X..
Mansfield, Anthony (1983), «Determining the thickness of graphs is NP-hard», Mathematical Proceedings of the Cambridge Philosophical Society93 (1): 9-23, MR684270, doi:10.1017/S030500410006028X..