Dunford–Pettis property

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In functional analysis, the Dunford–Pettis property, named after Nelson Dunford and B. J. Pettis, is a property of a Banach space stating that all weakly compact operators from this space into another Banach space are completely continuous. Many standard Banach spaces have this property, most notably, the space of continuous functions on a compact space and the space of the Lebesgue integrable functions on a measure space. Alexander Grothendieck introduced the concept in the early 1950s (Grothendieck 1953), following the work of Dunford and Pettis, who developed earlier results of Shizuo Kakutani, Kōsaku Yosida, and several others. Important results were obtained more recently by Jean Bourgain. Nevertheless, the Dunford–Pettis property is not completely understood.

Definition

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A Banach space   has the Dunford–Pettis property if every continuous weakly compact operator   from   into another Banach space   transforms weakly compact sets in   into norm-compact sets in   (such operators are called completely continuous). An important equivalent definition is that for any weakly convergent sequences   of   and   of the dual space   converging (weakly) to   and   the sequence   converges to  

Counterexamples

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  • The second definition may appear counterintuitive at first, but consider an orthonormal basis   of an infinite-dimensional, separable Hilbert space   Then   weakly, but for all     Thus separable infinite-dimensional Hilbert spaces cannot have the Dunford–Pettis property.
  • Consider as another example the space   where   The sequences   in   and   in   both converge weakly to zero. But  
  • More generally, no infinite-dimensional reflexive Banach space may have the Dunford–Pettis property. In particular, an infinite-dimensional Hilbert space and more generally, Lp spaces with   do not possess this property.

Examples

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See also

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References

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  • Bourgain, Jean (1981), "On the Dunford–Pettis property", Proceedings of the American Mathematical Society, 81 (2): 265–272, doi:10.2307/2044207, JSTOR 2044207
  • Grothendieck, Alexander (1953), "Sur les applications linéaires faiblement compactes d'espaces du type C(K)", Canadian Journal of Mathematics, 5: 129–173, doi:10.4153/CJM-1953-017-4
  • JMF Castillo, SY Shaw (2001) [1994], "Dunford–Pettis property", Encyclopedia of Mathematics, EMS Press
  • Lin, Pei-Kee (2004), Köthe-Bochner Function Spaces, Birkhäuser, ISBN 0-8176-3521-1, OCLC 226084233
  • Randrianantoanina, Narcisse (1997), "Some remarks on the Dunford-Pettis property" (PDF), Rocky Mountain Journal of Mathematics, 27 (4): 1199–1213, doi:10.1216/rmjm/1181071869, S2CID 15539667