Reflexive Space -- from Wolfram MathWorld
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Created, developed, and nurtured by Eric Weisstein at Wolfram Research
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Reflexive SpaceLet be a normed space and denote the second dual vector space of . The canonical map defined by gives an isometric linear isomorphism (embedding) from into . The space is called reflexive if this map is surjective. This concept was introduced by Hahn (1927). For example, finite-dimensional (normed) spaces and Hilbert spaces are reflexive. The space of absolutely summable complex sequences is not reflexive. James (1951) constructed a non-reflexive Banach space that is isometrically isomorphic to its second conjugate space. Reflexive spaces are Banach spaces. This follows since given a normed space that may or may not be Banach, the norm on induces a norm (called the dual norm) on the dual of , and under the dual norm, is Banach. Iterating again, (the bidual of ) is also Banach, and since is reflexive if it coincides with its bidual, is Banach.
SEE ALSO: Banach Space, Dual
Vector Space, Normed Space
Portions of this entry contributed by Mohammad Sal Moslehian Portions of this entry contributed by Christopher Stover Hahn, H. "Über lineare Gleichungssysteme in linearen Räumen." J. reine angew. Math. 157, 214-229, 1927. James, R. C. "A Non-Reflexive Banach Space Isometric with Its Second Conjugate Space." Proc. Nat. Acad. Sci. USA 37, 174-177, 1951. Moslehian, Mohammad Sal; Stover, Christopher; and Weisstein, Eric W. "Reflexive Space." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/ReflexiveSpace.html Wolfram Web Resources
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