Isosceles Trapezoid Peg Problem

Let a Jordan curve be a simple closed curve γR2\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.

Sources & referencesView supporting material

Primary source

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

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