Extensions of Vittas’ Theorem

The Greek architect Kostas Vittas published in 2006 a beautiful theorem (1) on the cyclic quadrilateral as follows: Theorem 1 (Kostas Vittas, 2006): If ABCD is a cyclic quadrilateral with P being the intersection of two diagonals AC and BD , then the four Euler lines of the triangles PAB , PBC , PCD and PDA are concurrent.