Mihai Cipu, Cyclic quadrilaterals associated with squares,
Forum Geometricorum, 11 (2011) 223--229.

Abstract.   We discuss a family of problems asking to find the geometrical locus of points P in the plane of a square ABCD having the property that the i-th triangle center in Kimberling's list with respect to triangles ABP, BCP, CDP, DAP are concyclic.

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