Abstract. Let K be a Hausdorff space and C b (K) be the Banach algebra of all complex bounded continuous functions on K. We study the Gâteaux and Fréchet differentiability of subspaces of C b (K). Using this, we show that the set of all strong peak functions in a nontrivial separating separable subspace H of C b (K) is a dense G δ subset of H, if K is compact. This gives a generalized Bishop's theorem, which says that the closure of the set of strong peak point for H is the smallest closed norming subset of H. The classical Bishop's theorem was proved for a separating subalgebra H and a metrizable compact space K.In the case that X is a complex Banach space with the Radon-Nikodým property, we show that the set of all strong peak functions inX is holomorphic} is dense. As an application, we show that the smallest closed norming subset of A b (B X ) is the closure of the set of all strong peak points for A b (B X ). This implies that the norm of A b (B X ) is Gâteaux differentiable on a dense subset of A b (B X ), even though the norm is nowhere Fréchet differentiable when X is nontrivial. We also study the denseness of norm attaining holomorphic functions and polynomials. Finally we investigate the existence of numerical Shilov boundary.
IntroductionLet K be a Hausdorff topological space. A function algebra A on K will be understood to be a closed subalgebra of C b (K) which is the Banach algebra of all bounded complex-valued continuous functions on K. The norm f of a bounded continuous function f on K is defined to be sup x∈K |f (x)|. A function algebra A is called separating if for two distinct points s, t in K, there is f ∈ A such that f (s) = f (t).In this paper, a subspace means a closed linear subspace. For each t ∈ K, let δ t be an evaluation functional onis called separating if for distinct points t, s in K we have αδ t = βδ s for any complex numbers α, β of modulus 1 as a linear functional on A. This definition of a separating subspace is a natural extension of the definition of a separating function algebra. In fact, given a separating function algebra A 2000 Mathematics Subject Classification. 46B04, 46G20, 46G25, 46B22.