A finite planar set is \(k\)-isosceles for \(k \geq 3\), if every \(k\)-point subset of the set contains a point equidistant from the other two. This paper gives a \(4\)-isosceles set consisting of \(7\) points with no three on a line and no four on a circle.
Citation
Xianglin Wei, Ren Ding. A \(4\)-isosceles \(7\)-point Set with Both Circle and Linear Restrictions[J], Ars Combinatoria, Volume 080. 189-191. .