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We show that toroidal polyhedral maps with four or more disjoint homotopic noncontractiblecircuits are not embeddable on the projective plane and that toroidal polyhedral maps with -veor more disjoint homotopic noncontractible circuits are not embeddable on the Klein bottle. Wealso show that the Klein bottle crossing numbers ofCm×Cn(m6n) form=3;4;5;6 are 1,2,4,and 6, respectively, and give upper bounds for all other values ofn. These crossing numbersdispla yat ypical behavior in that the value depends onl yonminstead of on bothmandnas isthe case for the plane and projective plane.
Riskin, A. (2001). On the nonembeddability and crossing numbers of some toroidal graphs on the Klein bottle. Discrete Mathematics, 234(1), 77–88. 10.1016/S0012-365X(00)00193-X