A finite planar set is \(k\)-isosceles for \(k \geq 3\) if every \(k\)-point subset of the set contains a point equidistant from two others. There exists no convex \(4\)-isosceles \(8\)-point set with \(8\) points on a circle.
Citation
Xianglin Wei. No \(4\)-Isosceles Set with Eight Points on a Circle[J], Ars Combinatoria, Volume 105. 77-81. .