**4. Conclusions**


Invariably, we did not consider some issues. In particular, based on the fact that the equation under consideration is autonomous, studying the equation on the phase plane is of significant interest and will be the subject of our further research.

**Author Contributions:** Conceptualization, A.I.L. and P.V.V.; data curation, A.V.S. and P.V.I.; formal analysis, A.I.L. and P.V.V.; investigation, Y.M.K. and P.V.I.; methodology, A.I.L. and Y.M.K.; project administration, V.V.K., V.G.E. and A.V.S.; resources, V.G.E. and A.V.S.; software, E.N.K.; supervision, V.V.K.; visualization, E.N.K.; writing—original draft, A.I.L.; writing—review and editing, V.V.K. and V.G.E. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by the Ministry of Education and Science of the Russian Federation within the framework of the program of activities of the world-class scientific and educational center "Rational Subsoil Use".

**Conflicts of Interest:** The authors declare no conflict of interest.
