In memory of the scientist Oleksandr Andriĭovych Boĭchuk (Q6648623)

A short description of the life and scientific results of Oleksandr Andriĭovych Boĭchuk (June 30, 1950 -- June 20, 2024) is presented. The scientific interests of O. A. Boĭchuk cover a wide range of complex problems of the theory of boundary value problems for systems of functional differential equations with a Noether operator. He classified resonant and non-resonant cases of such problems, developed perturbation theory, and found conditions for bifurcation of solutions of boundary value problems. O. A. Boĭchuk proposed the apparatus of generalized inverse operators for the study of such problems, which allowed him to significantly develop the qualitative theory of boundary value problems for such systems. He obtained a number of original results: criteria for the existence of solutions of linear and nonlinear systems of ordinary differential and difference equations is developed, algorithms for their construction were proposed; conditions of bifurcation and branching of solutions of such problems are obtained. See, for example, [\textit{A. A. Boichuk} and \textit{A. M. Samoilenko}, Generalized inverse operators and Fredholm boundary-value problems. 2nd edition. Berlin: De Gruyter (2016; Zbl 1394.47001)]; [\textit{A. A. Boĭchuk} and \textit{S. M. Chuĭko}, Constructive methods of analysis of boundary value problems of the theory of nonlinear oscillations. Kyïv: Naukova Dumka. 232 p. (2023) \url{doi:10.37863/6581477912-64})]; [\textit{A. A. Boĭchuk} and \textit{S. O. Pokutnyĭ}, Normally solvable boundary value problems for operator-differential equations. Kyïv: Naukova Dumka. 223 p. (2022), \url{https://imath.kiev.ua/monographs/3/monograph.pdf}].