New characterizations of Haj{\l}asz-Sobolev type spaces with variable   exponent on metric measure spaces
  In this article, we introduce classes of functions whose increment is controlled by the measure of a ball containing the corresponding points and a nonnegative function p(.) that is summable with respect to measure. These classes of functions can be considered as spaces with variable smoothness depending on the structure of the measure in a neighborhood of a given point. Moreover, we present several descriptions generalized classes of variable exponent Haj{\l}asz-Sobolev type on metric measure spaces by various maximal functions and we establish the equivalence between them. 
B.Cekic and R.A.Mashiyev
math.FA