Regularly oscillating mappings between metric spaces and a theorem of Hardy and Littlewood

This paper is motivated by the classical theorem due to Hardy and Littlewood which concerns analytic mappings on the unit disk and relates the growth of the derivative with the Hölder continuity. We obtain a version of this result in a very general setting – for regularly oscillating mappings on a metric space equipped with a weight, which is a continuous and positive function, with values in another metric space. As a consequence, we derive the Hardy and Littlewood theorem for analytic mappings on the unit ball of a normed space.