“…While non-local boundary conditions are widely researched for differential equations with integer order (see, e.g., [9,10]), less attention has been paid for fractional differential equations with non-local boundary conditions. We refer to papers [2,3,5,29], which are concerned with various existence results for fractional boundary value problems with non-local conditions. It is known that we usually cannot expect the solution of a fractional differential equation to be smooth on the whole interval of integration (see, e.g., [22,23]).…”