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Date: 7-7-2021
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Date: 15-5-2021
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Date: 4-7-2017
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A covering map (also called a covering or projection) is a surjective open map that is locally a homeomorphism, meaning that each point in
has a neighborhood that is the same after mapping
in
. In a covering map, the preimages
are a discrete set of
, and the cardinal number of
(which is possibly infinite) is independent of the choice of
.
For example, the map , as a map
, is a covering map in which
always consists of two points.
, where
is another example of a covering map, and is actually the universal cover of the torus
. If
is any covering of the torus, then there exists a covering
such that
factors through
, i.e.,
.
In contrast, as a map
(with the point
included) is not a true covering map, but rather a "branched covering."
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إدارة الغذاء والدواء الأميركية تقرّ عقارا جديدا للألزهايمر
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شراء وقود الطائرات المستدام.. "الدفع" من جيب المسافر
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العتبة العبّاسيّة: البحوث الّتي نوقشت في أسبوع الإمامة استطاعت أن تثري المشهد الثّقافي
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