[1] Ladas G. E., Lakshmikantham V.: Differential Equations in Abstract Spaces. Academic Press, New York, London 1972. MR 0460832
[2] Muszynski J.: Behaviour of Solutions of an Integral Equation. Časopis pro pěstování maternatiky, roč. 101 (1976), Praha, 327-342. MR 0445261 | Zbl 0351.45021