Coloring even-faced graphs in the torus and the Klein bottle
|Článek v odborném periodiku
|Časopis / Zdroj
|Combinatorica : an international journal of the János Bolyai Mathematical Society
|We prove that a triangle-free graph drawn in the torus with all faces bounded by even walks is 3-colorable if and only if it has no subgraph isomorphic to the Cayley graph C (Z(13); 1, 5). We also prove that a non-bipartite quadrangulation of the Klein bottle is 3-colorable if and only if it has no non-contractible separating cycle of length at most four and no odd walk homotopic to a non-contractible two-sided simple closed curve. These results settle a conjecture of Thomassen and two conjectures of Archdeacon, Hutchinson, Nakamoto, Negami and Ota.