“…Because of non-local behavior, fractional order boundary value problems are extensively applied to blood flow problems, control theory, the fluid-dynamic traffic model and polymer rheology. It implies that differential operators of arbitrary order can describe memory and hereditary properties of certain important processes [28][29][30][31]. There are many tools to deal with the uniqueness and multiplicity of solutions for fractional differential equations such as mixed monotone operators [23,[32][33][34], Avery-Peterson fixed point theorem [35,36], Guo-Krasnosel'skii fixed point theorem on a cone [37,38], the fixed point index theory [39][40][41], monotone iteration method [42], the critical point theory [43,44], Schauder's fixed point theory [45] and stability.…”