The quadripartite periodic square peg problem

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Let L>0L>0, and let CylL\mathtt{Cyl}_L be the cylinder obtained from R2\mathbb{R}^2 by identifying points differing by (L,0)(L,0). Let Graph0,L ⁣:R/LZ→CylL\mathtt{Graph}_{0,L}\colon\mathbb{R}/L\mathbb{Z}\to\mathtt{Cyl}_L be the standard closed curve t↦(t,0)t\mapsto(t,0). For four subsets of the cylinder, say that they jointly inscribe a square if their Cartesian product intersects the closure of the space of squares in CylL\mathtt{Cyl}_L; equivalently, there are x∈R/LZx\in\mathbb{R}/L\mathbb{Z} and y,a,b∈Ry,a,b\in\mathbb{R} such that the four points (x,y)(x,y), (x+a,y+b)(x+a,y+b), (x+a−b,y+a+b)(x+a-b,y+a+b), and (x−b,y+a)(x-b,y+a) lie in the four sets in order. Let σ1,σ2 ⁣:R/LZ→CylL\sigma_1,\sigma_2\colon\mathbb{R}/L\mathbb{Z}\to\mathtt{Cyl}_L be simple closed curves homologous to Graph0,L\mathtt{Graph}_{0,L}.

Quadripartite periodic square peg conjecture. The quadruplet

(σ1(R/LZ),σ1(R/LZ),σ2(R/LZ),σ2(R/LZ))\bigl(\sigma_1(\mathbb{R}/L\mathbb{Z}),\sigma_1(\mathbb{R}/L\mathbb{Z}),\sigma_2(\mathbb{R}/L\mathbb{Z}),\sigma_2(\mathbb{R}/L\mathbb{Z})\bigr)

jointly inscribes a square.

This claim would imply the periodic square peg problem and allows degenerate inscribed squares through the closure formulation. It is presented as an open conjecture.

References

Primary source

Terence Tao, “An integration approach to the Toeplitz square peg problem”, arXiv:1611.07441 (2017).

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