Approximating z-bar in the Bergman space

We consider the problem of finding the best approximation to $\bar{z}$ in the Bergman Space $A^{2}(Ω)$. We show that this best approximation is the derivative of the solution to the Dirichlet problem on $\partialΩ$ with data $\left|z\right|^{2}$ and give examples of domains where the best approximation is a polynomial, or a rational function. Finally, we obtain the "isoperimetric sandwich" for $dist(\overline{z},Ω)$ that yields the celebrated St. Venant inequality for torsional rigidity.

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