$K_6$-Minors in Triangulations on the Klein Bottle
Ken‐ichi Kawarabayashi, Raiji Mukae, Atsuhiro Nakamoto · SIAM Journal on Discrete Mathematics · 2008
In this paper, we shall characterize triangulations on the Klein bottle without $K_6$-minors. Our characterization implies that every 5-connected triangulation on the Klein bottle has a $K_6$-minor. The connectivity “5" is best possible in a sense that there is a 4-connected triangulation on the Klein bottle without $K_6$-minors.