A new characterization for Meir-Keeler condensing operators and its applications

Darbo's fixed point theorem and its generalizations play a crucial role in the existence of solutions in integral equations. Meir-Keeler condensing operators is a generalization of Darbo's fixed point theorem and most of other generalizations are a special case of this result. In recent years, some authors applied these generalizations to solve several special integral equations and some of them presented a characterization for Meir-Keeler condensing operators, which needs L-functions. But, finding an appropriate L-function needs more struggle. In this paper, we give a characterization for Meir-Keeler condensing operators via measure of non-compactness. Current characterization presents a criterion by which we can show that if a given generalization of Darbo's fixed point theorem is Meer-Keeler condensing or not. Ultimately, we give several corollaries and point out several generalizations of Darbo's fixed point theorem and show that all of them are Meir-Keeler condensing operator or a special case of this result.