There are a number of generalizations of metric spaces and Banach contraction
principle. In this sequel, Bakhtin [2] and Czerwik [9] introduced b-metric
spaces as a generalization of metric spaces. They proved the contraction mapping
principle in b-metric spaces that generalized the famous Banach contraction
principle in such spaces. Since then, several papers have dealt with
fixed point theory or the variational principle for single-valued and multivalued
operators in b-metric spaces (see, e.g., [1,3–6,9,10] and the references
therein).