Duality and distance formulas in spaces defined by means of oscillation

For the classical space of functions with bounded mean oscillation, it is well known that and there are many characterizations of the distance from a function f in to . 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 Mobius invariant spaces such as Q (K) -spaces, weighted spaces, Lipschitz-Holder spaces and rectangular of several variables.