The quadripartite periodic square peg problem

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/LZCylL\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 xR/LZx\in\mathbb{R}/L\mathbb{Z} and y,a,bRy,a,b\in\mathbb{R} such that the four points (x,y)(x,y), (x+a,y+b)(x+a,y+b), (x+ab,y+a+b)(x+a-b,y+a+b), and (xb,y+a)(x-b,y+a) lie in the four sets in order. Let σ1,σ2 ⁣:R/LZCylL\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.

Sources & referencesView supporting material

Primary source

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

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