The odd triangle ring puzzle problem
Sylvain Barré, Othmane Oukrid, Mikaël Pichot
TL;DR
The paper solves the odd triangle ring puzzle problem associated with the unique odd Moebius–Kantor complex using the method of Sidon sequences, identifying a complete classification into three families: two uncountable families formed by unions of height-1 or height-2 flat strips of period $6$, and a finite family of twelve exceptional puzzles. It advances the study by introducing root distributions and the mesoscopic-rank framework within a CAT(0) 2-complex setting to translate local constraints into global tessellation structure. The main result demonstrates that puzzle solutions organize into the three families and provides explicit constructions and counts for each, notably the twelve exceptional cases arising from the special distribution $D_0$. This approach deepens the connection between geometric group theory, CAT(0) geometry, and combinatorial tiling problems, with potential implications for understanding Sidon-type puzzle problems in related complexes.
Abstract
Ring puzzles are tessellations of the Euclidean plane respecting local constraints around vertices. Such puzzles may arise in geometric group theory, for example, as embedded flat planes in certain CAT(0) complexes of dimension 2. In the present paper, we solve the odd ring puzzle problem, which is associated with the unique odd Moebius--Kantor CAT(0) complex by the method of Sidon sequences. We prove that there are precisely three families of such puzzles, two uncountable families, and a finite family of twelve exceptional puzzles.
