映射度{\displaystyle [S^{n},S^{n}]=\pi _{n}S^{n}\to \mathbf {Z} } 。 拓扑度数理论(英语:Topological degree theory) Flanders, H. Differential forms with applications to the physical
完全圖(原始内容存档于2020-02-20) (英语). Tichy, Robert F.; Wagner, Stephan, Extremal problems for topological indices in combinatorial chemistry (PDF), Journal of Computational Biology