In mathematics, a Grothendieck space, named after Alexander Grothendieck, is a Banach space X such that for all separable Banach spaces Y, every bounded linear operator from X to Y is weakly compact, that is, the image of a bounded subset of X is a weakly compact subset of Y.
Every reflexive Banach space is a Grothendieck space. Conversely, a separable Grothendieck space X must be reflexive, since the identity from X to X is weakly compact in this case.
Grothendieck spaces which are not reflexive include the space C(K) of all continuous functions on a Stonean compact space K, and the space L∞(μ) for a positive measure μ (a Stonean compact space is a Hausdorff compact space in which the closure of every open set is open).
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