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4 equal circles touch diagonals and internally circumcircle of ABCD

Source: 2009 Sharygin Geometry Olympiad Final Round problem 8 grade 9

July 26, 2018
geometrycircumcirclecyclic quadrilateralcircles

Problem Statement

Given cyclic quadrilateral ABCDABCD. Four circles each touching its diagonals and the circumcircle internally are equal. Is ABCDABCD a square?
(C.Pohoata, A.Zaslavsky)