... study the existence of solutions for a class of fractional differential equations. Due to thesingularity of the possible solutions, we introduce a new and proper concept of periodic boundaryvalue ... u0u0,butlimt→0t1−δutu0. Hence, to study the periodic boundary value problem, one has toconsider the following boundary condition of periodic typelimt→0t1−δut u1. ... 1.3.36which is precisely Green’s function for the periodic boundary value problem considered in25, 26.10 Boundary Value ProblemsProof. a We check, using hypothesis 4.3,thatBu ∈ C1−δ0, 1, for...