| 翻訳と辞書 | cylinder set| cylinder set  : ウィキペディア英語版 | 
 In mathematics, a cylinder set is the natural open set of a product topology. Cylinder sets are particularly useful in providing the base of the natural topology of the product of a countable number of copies of a set.  If ''V'' is a finite set, then each element of ''V'' can be represented by a letter, and the countable product can be represented by the collection of strings of letters.
 ==General definition==
 Consider the cartesian product  of topological spaces , indexed by some index . The canonical projection is the function  that maps every element of the product to its  component. Then, given any open set , the preimage  is called an open cylinder.  The intersection of a finite number of open cylinders is a cylinder set. The collection of open cylinders form a subbase of the product topology on ; the collection of all cylinder sets thus form a basis.
 The restriction that the cylinder set be the intersection of a finite number of open cylinders is important; allowing infinite intersections generally results in a finer topology. In this case, the resulting topology is the box topology; cylinder sets are never Hilbert cubes.
 
 抄文引用元・出典: フリー百科事典『 ウィキペディア(Wikipedia)』
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