[1]
Ronto, A.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 (Nov. 2003), 1541-1568.