Quadratic bound between surface crossing numbers

Let GG be a graph, and for a surface [200 Σ[200~\Sigma let iocrΣ(G)\mathop{\rm iocr}\nolimits_{\Sigma}(G) denote the fewest number of pairs of independent edges that cross oddly in a drawing of GG on Σ\Sigma, while crΣ(G)\mathop{\rm cr}\nolimits_{\Sigma}(G) denotes the crossing number on Σ\Sigma. Quadratic surface crossing-number conjecture. For Σ\Sigma equal to the projective plane or the torus, one has

crΣ(G)(2iocrΣ(G)2).\mathop{\rm cr}\nolimits_{\Sigma}(G) \leq \binom{2\mathop{\rm iocr}\nolimits_{\Sigma}(G)}{2}.

The corresponding inequality is known for the plane, but analogous bounds are not known for other surfaces, including the projective plane and torus, so this proposes a concrete quadratic bound in those cases.

Sources & referencesView supporting material

Primary source

Radoslav Fulek, Michael J. Pelsmajer and Marcus Schaefer, “Strong Hanani-Tutte for the Torus”, arXiv:2009.01683 (2021).

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