Isosceles Trapezoid Peg Problem
Let a Jordan curve be a simple closed curve . An isosceles trapezoid is a quadrilateral whose vertices are the intersection set of two parallel lines and a circle; a curve inscribes a polygon if it contains four points forming a polygon similar to 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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