1. North-Holland Mathematics Studies;AA Kilbas,2006
2. Lecture Notes in Mathematics;K Diethelm,2010
3. Henderson, J., Luca, R.: Boundary Value Problems for Systems of Differential, Difference and Fractional Equations: Positive Solutions. Elsevier, Netherlands (2016)
4. Almuthaybiri, S.S., Tisdell, C.C.: Uniqueness of solutions for a coupled system of nonlinear fractional differential equations via weighted norms. Commun. Appl. Nonlinear Anal. 28(1), 65–76 (2021)
5. Asif, N.A., Khan, R.A.: Positive solutions to singular system with four-point coupled boundary conditions. J. Math. Anal. Appl. 386, 848–861 (2012)