The periodic coloring conjecture

Let N1N\geqslant 1, let VV be a finite set of primitive, nonzero, mutually incommensurable vectors in Z2\mathbb{Z}^2, let Σ\Sigma be a finite color set, and let ΩΣV×(Z/NZ)2\Omega\subset \Sigma^{|V|}\times (\mathbb{Z}/N\mathbb{Z})^2. For each vVv\in V, choose a fixed primitive vector vˉ\bar v orthogonal to vv. Let Coloring(V,N,Σ,Ω)\operatorname{Coloring}(V,N,\Sigma,\Omega) be the set of tuples of functions Cv ⁣:ZΣC_v\colon\mathbb{Z}\to\Sigma satisfying the local condition specified by the source, using a two-dimensional clock σ ⁣:(Z/NZ)2(Z/NZ)2\sigma\colon(\mathbb{Z}/N\mathbb{Z})^2\to(\mathbb{Z}/N\mathbb{Z})^2.

Periodic coloring conjecture. For any VV, NN, Σ\Sigma, and Ω\Omega as above, the solution set Coloring(V,N,Σ,Ω)\operatorname{Coloring}(V,N,\Sigma,\Omega) is not aperiodic.

This conjecture is presented as an equivalent reformulation of the periodic tiling conjecture in virtually-Z2\mathbb{Z}^2 spaces. The source gives no resolution status.

Sources & referencesView supporting material

Primary source

Rachel Greenfeld, “Translational tilings: structured or wild?”, arXiv:2509.25576 (2025).

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