Nikolai Nikolaevich Dobrovol’sky
Tula State University; Tula State L. N. Tolstoy Pedagogical University, Tula
Russian Federation

candidate of physical and mathematical sciences, assistant of the department of applied mathematics and computer science, Tula State University; associate Professor of algebra, mathematical analysis and geometry, Tula State L. N. Tolstoy Pedagogical University, Tula.

Mikhail Nikolaevich Dobrovol’skii
Geophysical centre of RAS, Moscow
Russian Federation

candidate of candidate of physical and mathematical sciences, senior researcher

Nikolai Mihailovich Dobrovol’skii
Tula State L. N. Tolstoy Pedagogical University, Tula
Russian Federation

doctor of physical and mathematical sciences, professor, head of the department of algebra, mathematical analysis and geometry

Irina Nikolaevna Balaba
Tula State L. N. Tolstoy Pedagogical University, Tula
Russian Federation

doctor of physical and mathematical sciences, assistant professor, professor of the department of algebra, mathematical analysis and geometry

Irina Yuryevna Rebrova
Tula State L. N. Tolstoy Pedagogical University, Tula
Russian Federation

candidate of physical and mathematical Sciences, associate professor, dean of the faculty of mathematics, physics and computer science