Grothendieck space

Summary

In mathematics, a Grothendieck space, named after Alexander Grothendieck, is a Banach space in which every sequence in its continuous dual space that converges in the weak-* topology (also known as the topology of pointwise convergence) will also converge when is endowed with which is the weak topology induced on by its bidual. Said differently, a Grothendieck space is a Banach space for which a sequence in its dual space converges weak-* if and only if it converges weakly.

Characterizations edit

Let   be a Banach space. Then the following conditions are equivalent:

  1.   is a Grothendieck space,
  2. for every separable Banach space   every bounded linear operator from   to   is weakly compact, that is, the image of a bounded subset of   is a weakly compact subset of  
  3. for every weakly compactly generated Banach space   every bounded linear operator from   to   is weakly compact.
  4. every weak*-continuous function on the dual   is weakly Riemann integrable.

Examples edit

  • Every reflexive Banach space is a Grothendieck space. Conversely, it is a consequence of the Eberlein–Šmulian theorem that a separable Grothendieck space   must be reflexive, since the identity from   is weakly compact in this case.
  • Grothendieck spaces which are not reflexive include the space   of all continuous functions on a Stonean compact space   and the space   for a positive measure   (a Stonean compact space is a Hausdorff compact space in which the closure of every open set is open).
  • Jean Bourgain proved that the space   of bounded holomorphic functions on the disk is a Grothendieck space.[1]

See also edit

References edit

  1. ^ J. Bourgain,   is a Grothendieck space, Studia Math., 75 (1983), 193–216.
  • J. Diestel, Geometry of Banach spaces, Selected Topics, Springer, 1975.
  • J. Diestel, J. J. Uhl: Vector measures. Providence, R.I.: American Mathematical Society, 1977. ISBN 978-0-8218-1515-1.
  • Shaw, S.-Y. (2001) [1994], "Grothendieck space", Encyclopedia of Mathematics, EMS Press
  • Khurana, Surjit Singh (1991). "Grothendieck spaces, II". Journal of Mathematical Analysis and Applications. 159 (1). Elsevier BV: 202–207. doi:10.1016/0022-247x(91)90230-w. ISSN 0022-247X.
  • Nisar A. Lone, on weak Riemann integrability of weak* - continuous functions. Mediterranean journal of Mathematics, 2017.