The group of automorphisms of $L_{\infty} $ is algebraically reflexive

Volume 161 / 2004

Félix Cabello Sánchez Studia Mathematica 161 (2004), 19-32 MSC: Primary 46L40. DOI: 10.4064/sm161-1-2


We study the reflexivity of the automorphism (and the isometry) group of the Banach algebras $L_\infty (\mu )$ for various measures $\mu $. We prove that if $\mu $ is a non-atomic $\sigma $-finite measure, then the automorphism group (or the isometry group) of $L_\infty (\mu )$ is [algebraically] reflexive if and only if $L_\infty (\mu )$ is $^*$-isomorphic to $L_\infty [0,1]$. For purely atomic measures, we show that the group of automorphisms (or isometries) of $\ell _\infty ({\mit \Gamma })$ is reflexive if and only if ${\mit \Gamma }$ has non-measurable cardinal. So, for most “practical" purposes, the automorphism group of $\ell _\infty ({\mit \Gamma })$ is reflexive.


  • Félix Cabello SánchezDepartamento de Matemáticas
    Universidad de Extremadura
    Avenida de Elvas
    06071 Badajoz, Spain

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