Kotvytskiy, A. T., S. D. Bronza, and S. R. Vovk. “Estimating the Number of Solutions Equation of N-Point Gravitational Lenses Algebraic Geometry Methods”. Journal of V. N. Karazin Kharkiv National University. Series Physics, no. 24, Jan. 2017, pp. 54-58, https://periodicals.karazin.ua/physics/article/view/9208.