Isosceles Trapezoid Peg Problem

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Let a Jordan curve be a simple closed curve γ⊂R2\gamma\subset\mathbb{R}^2. An isosceles trapezoid is a quadrilateral whose vertices are the intersection set of two parallel lines and a circle; a curve inscribes a polygon PP if it contains four points forming a polygon similar to PP under an orientation-preserving similarity. Isosceles Trapezoid Peg Problem. Every Jordan curve inscribes every isosceles trapezoid. This is a generalisation of the Square Peg Problem and remains an open question in the stated generality, although the paper establishes the claim for smooth Jordan curves and additional nonsmooth cases.

References

Primary source

Adam Barber, “Inscriptions of Isosceles Trapezoids in Jordan Curves”, arXiv:2604.27717 (2026).

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