Schiffer comparison operators and approximations on Riemann surfaces bordered by quasicircles

We consider a compact Riemann surface $R$ of arbitrary genus, with a finite number of non-overlapping quasicircles, which separate $R$ into two subsets: a connected Riemann surface $\mathrm{\Sigma }$, and the union $\mathcal{O}$ of a finite collection of simply-connected regions. We prove that the Schiffer integral operator mapping the Bergman space of anti-holomorphic one-forms on $\mathcal{O}$ to the Bergman space of holomorphic forms on $\mathrm{\Sigma }$ is an isomorphism. We then apply this to prove versions of the Plemelj-Sokhotski isomorphism and jump decomposition for such a configuration. Finally we obtain some approximation theorems for the Bergman space of one-forms and Dirichlet space of holomorphic functions on $\mathrm{\Sigma }$ by elements of Bergman space and Dirichlet space on fixed regions in $R$ containing $\mathrm{\Sigma }$.