On a Necessary and Sufficient Cyclicity Condition for a Quadrilateral.
A convex quadrilateral with sides a, b, c, d and diagonals p, q is cyclic iff abp-bcq+cdp-daq = 0. This condition, in spite of its simplicity, appears to be unnoted and unexpectedly proof-resilient. We employ advanced methods of computer algebra and nonlinear analysis.
Publication language:russian, pages:18
Mathematical problems and theory of numerical methods