Approximation numbers of composition operators on the Dirichlet space
Approximation numbers of composition operators on the Dirichlet space
We study the decay of approximation numbers of compact composition operators on the Dirichlet space. We give upper and lower bounds for these numbers. In particular, we improve on a result of El-Fallah, Kellay, Shabankhah and Youssfi, on the set of contact points with the unit circle of a compact …