1. A.A. Kilbas, H.M. Srivastava, J.J. Trujillo.(2006), Theory and Applications of Fractional Differential Equations, in: North-Holland Mathematics Studies, vol. 204, Elsevier Science BV, Amsterdam.
2. K.S.Miller, B.Ross.(1993), An Introduction to the Fractional Calculus and Differential Equations, John Wiley, New York.
3. C. Corduneanu.(2002), Functional Equations with Causal Operators, in: Stability and Control: Theory, Methods and Applications, vol. 16, Taylor Francis, London.
4. V. Lakshmikantham, S. Leela, Z. Drici, F.A. McRae.(2010), Theory of Causal Differential Equations, Atlantis Stud. Math. Eng. Sci. vol. 5, World Scientific, Singapore.
5. T. Jankowski.(2008), Boundary value problems with causal operators, Nonlinear Anal.68, 3625-3632. 10.1016/j.na.2007.04.005