Radon-Nikodym theorem in spaces of measures.
We give a quantitative characterization of the pairs of weights for which the dyadic version of the one-sided Hardy-Littlewood maximal operator satisfies a restricted weak type inequality for . More precisely, given any measurable set , the estimate holds if and only if the pair belongs to , that is, for every dyadic cube and every measurable set . The proof follows some ideas appearing in S. Ombrosi (2005). We also obtain a similar quantitative characterization for the non-dyadic...