Extremal problems in Bergman spaces and an extension of Ryabykh's Hardy space regularity theorem for 1 < p < infinity

We study linear extremal problems in the Bergman space $A^p$ of the unit disc, where $1 < p < \infty$. Given a functional on the dual space of $A^p$ with representing kernel $k \in A^q$, where $1/p + 1/q = 1$, we show that if $q \le q_1 < \infty$ and $k \in H^{q_1}$, then $F \in H^{(p-1)q_1}$. This result was previously known only in the case where $p$ is an even integer. We also discuss related results.