1. 1. M. S. Agranovich, M. I. Vishik, "Elliptic problems with a parameter and parabolic problems of general type," Uspekhi Mat. Nauk, 19, No. 3(117), 53-161 (1964)
2. English translation: Russ. Math. Surv., 19, No. 3, 53-157 (1964), https://doi.org/10.1070/RM1964v019n03ABEH001149
3. 2. V. I. Bogachev, N. V. Krylov, M. Röckner, S. V. Shaposhnikov, Fokker-Planck-Kolmogorov Equations [in Russian], Inst. Komp. Issled., Moscow (2013)
4. [in English] Am. Math. Soc. (2015).
5. 3. O. H. Voznyak, S. D. Ivasyshen, I. P. Medyns'kyi, "On the fundamental solution of the Cauchy problem for Kolmogorov ultraparabolic equation with degeneration in the initial plane," Bukov. Mat. Zh., 3, No. 3-4, 41-51 (2015) (in Ukrainian).