“…$$ where
,
,
is the Caputo fractional derivative and
is a continuous function, establishing the existence of positive solutions with the help of the Guo–Krasnoselskii fixed point theorem
9 . Given the fact that problems with integral boundary conditions arise naturally in many applied fields of science, like thermal conduction problems, semiconductor problems, chemical engineering, blood flow problems, underground water problems, hydrodynamic problems and population dynamics, and include multipoint and nonlocal integral boundary value conditions as special cases, the work of Cabada and Wang
9 originated a strong research on integral boundary value problems of nonlinear multiterm fractional differential equations; see, for example, previous studies
10–13 . Among recent methods that are useful for such kind of fractional differential equations, we can mention the monotone iterative technique,
14 the topological degree theory,
15 and fixed point approaches
16,17 …”