“…We start with some useful definitions and basic lemmas concerned with the fractional calculus. For more details, the reader may refer to Bai and Zhang 17 and Su and Zhang 7 . We denote by C [0,1] the Banach space of all continuous functions on [0,1] with the sup‐norm and L 1 [0,1] stands for the Banach space of measurable functions that are Lebesgue integrable on [0,1] with the norm .…”