Best Approximation in the Mean by Analytic and Harmonic Functions

For n ≥ 2, let Bn denote the unit ball in R, and for p ≥ 1 let L denote the Banach space of p-summable functions on Bn. Let L p h(Bn) denote the subspace of harmonic functions on Bn that are p-summable. When n = 2, we often write D instead of B2, and we let A denote the Bergman space of analytic functions in L. Let ω be a function in L. We are interested in finding the best approximation to ω in A and Lph(Bn). Existence of a best approximant is straighforward; this paper considers the following two qualitative properties: