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This page was last edited on 11 September 2006, at 05:09 (UTC).; Text is available under the Creative Commons Attribution-ShareAlike 4.0 License; additional terms may apply.
Cover, a pair in the covering relation of a partially ordered set, or the greater element in such a pair; Cover, in database theory, an equivalent set of constraints; Land cover, physical material on the surface of the earth; Concrete cover, in engineering, distance between reinforcement and the outer surface of element
A good cover is an open cover in which all sets and all non-empty intersections of finitely-many sets are contractible (Petersen 2006). The concept was introduced by André Weil in 1952 for differentiable manifolds , demanding the U α 1 … α n {\displaystyle U_{\alpha _{1}\ldots \alpha _{n}}} to be differentiably contractible.