Valentin Gushchin, Adam Khasanov. "THE LEVEL SURFACE OF THE GENERALIZED PROBLEM OF TWO CENTERS." SGEM International Multidisciplinary Scientific GeoConference EXPO Proceedings; 17th International Multidisciplinary Scientific GeoConference SGEM2017, Informatics, Geoinformatics and Remote Sensing, 2017, pp. 673-680. https://doi.org/10.5593/sgem2017/22/s09.085