Noncoherent uniform algebras in $\mathbb {C}^n$

Tom 234 / 2016

Raymond Mortini Studia Mathematica 234 (2016), 83-95 MSC: Primary 32A38; Secondary 46J15, 46J20, 30H05, 13J99. DOI: 10.4064/sm8517-5-2016 Opublikowany online: 20 June 2016


Let $\mathbf D=\overline {\mathbb {D}}$ be the closed unit disk in $\mathbb C$ and $\mathbf {B}_n=\overline {\mathbb {B}}_n$ the closed unit ball in $\mathbb C^n$. For a compact subset $K$ in $\mathbb C^n$ with nonempty interior, let $A(K)$ be the uniform algebra of all complex-valued continuous functions on $K$ that are holomorphic in the interior of $K$. We give short and non-technical proofs of the known facts that $A(\overline {\mathbb D}^n)$ and $A(\mathbf B_n)$ are noncoherent rings. Using, additionally, Earl’s interpolation theorem in the unit disk and the existence of peak functions, we also establish with the same method the new result that $A(K)$ is not coherent. As special cases we obtain Hickel’s theorems on the noncoherence of $A(\overline \varOmega )$, where $\varOmega $ runs through a certain class of pseudoconvex domains in $\mathbb C^n$, results that were obtained with deep and complicated methods. Finally, using a refinement of the interpolation theorem we show that no uniformly closed subalgebra $A$ of $C(K)$ with $P(K)\subseteq A\subseteq C(K)$ is coherent provided the polynomial convex hull of $K$ has no isolated points.


  • Raymond MortiniUniversité de Lorraine
    Institut Élie Cartan de Lorraine, UMR 7502
    F-57045 Metz, France

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