|
In functional analysis, a branch of mathematics, the Goldstine theorem, named after Herman Goldstine, is stated as follows: :Goldstine Theorem. Let be a Banach space, then the image of the closed unit ball under the canonical embedding into the closed unit ball of the bidual space is weak *-dense. The conclusion of the theorem is not true for the norm topology, which can be seen by considering the Banach space of real sequences that converge to zero, , and its bi-dual space . == Proof == Given , an -tuple of linearly independent elements of and a we shall find in such that for . If the requirement is dropped, the existence of such an follows from the surjectivity of : Now let : Every element of has the required property, so that it suffices to show that the latter set is not empty. Assume that it is empty. Then and by the Hahn-Banach theorem there exists a linear form such that and . Then and therefore : which is a contradiction. 抄文引用元・出典: フリー百科事典『 ウィキペディア(Wikipedia)』 ■ウィキペディアで「Goldstine theorem」の詳細全文を読む スポンサード リンク
|