Rafla's conjecture on crossing-free Hamiltonian cycles in simple drawings

Let KnK_n be the complete graph, and let a simple drawing be a drawing in which any two edges have at most one common point and no two edges incident to the same vertex cross. A crossing-free Hamiltonian cycle is a cycle that visits every vertex exactly once and whose edges do not cross. Rafla's conjecture. Every simple drawing of KnK_n with n3n \geq 3 vertices contains a crossing-free Hamiltonian cycle.

This conjecture asks whether the familiar property of straight-line drawings of complete graphs extends to all simple drawings. It was conjectured by Rafla in 1988; the supplied text gives no evidence of a general resolution, although it records proofs for several restricted drawing classes.

Sources & referencesView supporting material

Primary source

Oswin Aichholzer, Joachim Orthaber and Birgit Vogtenhuber, “Separable Drawings: Extendability and Crossing-Free Hamiltonian Cycles”, arXiv:2410.09922 (2026).

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