The essential norm of a composition operator on a planar domain
We generalize to nitely connected planar domains the result of Joel Shapiro which gives a formula for the essential norm of a composition operator. In the process, we dene and give some properties of a generalization of the Nevanlinna counting function and prove generalizations of the Littlewood inequality, the Littlewood{Paley identity, and change of variable formulas, as well.