On the existence of almost greedy bases in Banach spaces

Tom 159 / 2003

S. J. Dilworth, N. J. Kalton, Denka Kutzarova Studia Mathematica 159 (2003), 67-101 MSC: Primary 46B15; Secondary 41A65, 46B20. DOI: 10.4064/sm159-1-4


We consider several greedy conditions for bases in Banach spaces that arise naturally in the study of the Thresholding Greedy Algorithm (TGA). In particular, we continue the study of almost greedy bases begun in [3]. We show that almost greedy bases are essentially optimal for $n$-term approximation when the TGA is modified to include a Chebyshev approximation. We prove that if a Banach space $X$ has a basis and contains a complemented subspace with a symmetric basis and finite cotype then $X$ has an almost greedy basis. We show that $c_0$ is the only ${\mathcal L}_\infty $ space to have a quasi-greedy basis. The Banach spaces which contain almost greedy basic sequences are characterized.


  • S. J. DilworthDepartment of Mathematics
    University of South Carolina
    Columbia, SC 29208, U.S.A.
  • N. J. KaltonDepartment of Mathematics
    University of Missouri
    Columbia, MO 65211, U.S.A.
  • Denka KutzarovaInstitute of Mathematics
    Bulgarian Academy of Sciences
    Sofia, Bulgaria
    Department of Mathematics
    University of Illinois at Urbana-Champaign
    Urbana, IL 61801, U.S.A.

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