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The analytic content is not semiadditive

  • Eduardo S. Zeron,
  • Paul M. Gauthier

摘要

We show that the analytic content \(\lambda (\cdot )\) λ ( · ) is neither subadditive nor semiadditive. To be precise, for compact sets K in the complex plane, \(\lambda (K)\) λ ( K ) is the K-uniform distance from the complex conjugation to the algebra of all rational functions with poles outside K. Thus, given any integer \(n\ge 1\) n 1 , it is proven that each compactum K can be decomposed as the union of two new compact sets \(E_1\) E 1 and \(E_2\) E 2 with \(\lambda (E_j)\le 1/n\) λ ( E j ) 1 / n for \(j=1,2\) j = 1 , 2 . Moreover, we also show that no compactum K with positive analytic content can be decomposed as the countable union of compact sets of zero analytic content.