RontoA. M. (2003). Exact Solvability Conditions for the Cauchy Problem for Systems of First-Order Linear Functional-Differential Equations Determined by $(σ_1, σ_2, . , σ_n; τ)$-Positive Operators. Ukrains’kyi Matematychnyi Zhurnal, 55(11), 1541-1568. Retrieved from https://umj.imath.kiev.ua/index.php/umj/article/view/4023