Uniqueness conjecture for the toroidal penny graph embedding of K3,3K_{3,3}

A toroidal penny graph is a contact graph of congruent non-overlapping disks embedded on a flat torus, with vertices representing disk centers and edges representing tangent pairs. Consider the embedding of K3,3K_{3,3} whose toroidal coordinates are given by

(1336,1336),(1136,136),(136,1136),(1336,1336),(1136,136),(136,1136).\left(\frac{13}{36},-\frac{13}{36}\right), \left(\frac{11}{36},\frac{1}{36}\right), \left(\frac{1}{36},\frac{11}{36}\right), \left(-\frac{13}{36},\frac{13}{36}\right), \left(-\frac{11}{36},-\frac{1}{36}\right), \left(-\frac{1}{36},-\frac{11}{36}\right).

Uniqueness conjecture for the K3,3K_{3,3} embedding. The proposed embedding of K3,3K_{3,3}, with coordinates as described in the table, is unique up to an isometry.

The claim concerns the rigidity of the exhibited toroidal penny graph realization of K3,3K_{3,3}: no non-isometric embedding with the same graph is expected to exist. The source provides the embedding and its packing radius but gives no resolution of this uniqueness question.

Sources & referencesView supporting material

Primary source

Cédric Lorand, “K5 and K3,3 are Toroidal Penny Graphs”, arXiv:2410.10673 (2024).

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