Duality and Distance Formulas in Spaces Defined by Means of Oscillation

Abstract: For the classical space of functions with bounded mean oscillation, it is well known that VMO** = BMO and there are many characterizations of the distance from a function f in BMO to VMO. When considering the Bloch space, results in the same vein are available with respect to the little Bloch space. In this paper such duality results and distance formulas are obtained by pure functional analysis. Applications include general M\"obius invariant spaces such as Q_K-spaces, weighted spaces, Lipschitz-H\"older spaces and rectangular BMO of several variables.