Infinitely many triangle-minimizing digon-free pseudocircle arrangements

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Let nn be a positive integer, and let a digon-free intersecting arrangement be an arrangement of nn pseudocircles in which every pair intersects and no cell is a digon. Let p3(A)p_3(\mathcal{A}) denote the number of triangular cells of an arrangement A\mathcal{A}. Triangle-minimization conjecture. There are digon-free intersecting arrangements A\mathcal{A} of nn pseudocircles satisfying

p3(A)=⌈4n3⌉p_3(\mathcal{A})=\left\lceil\frac{4n}{3}\right\rceil

for infinitely many values of nn. The bound ⌈4n/3⌉\lceil 4n/3\rceil is known and is reported to be attained for 6≤n≤146\leq n\leq14; the conjecture asks for infinitely many attaining values.

References

Primary source

Stefan Felsner and Manfred Scheucher, “Arrangements of Pseudocircles: Triangles and Drawings”, arXiv:1708.06449 (2020).

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