Metacompact space

In mathematics, in the field of general topology, a topological space is said to be metacompact if every open cover has a point finite open refinement. That is, given any open cover of the topological space, there is a refinement which is again an open cover with the property that every point is contained only in finitely many sets of the refining cover.

A space is countably metacompact if every countable open cover has a point finite open refinement.

Properties

The following can be said about metacompactness in relation to other properties of topological spaces:

• Every paracompact space is metacompact. This implies that every compact space is metacompact, and every metric space is metacompact. The converse does not hold: a counter-example is the Dieudonné plank.
• Every metacompact space is orthocompact.
• Every metacompact normal space is a shrinking space
• The product of a compact space and a metacompact space is metacompact. This follows from the tube lemma.
• An easy example of a non-metacompact space (but a countably metacompact space) is the Moore plane.
• In order that a Tychonoff space X is compact it is necessary and sufficient that X is metacompact and pseudocompact (see Watson).

Covering dimension

A topological space X is said to be of covering dimension n if every open cover of X has a point finite open refinement such that no point of X is included in more than n + 1 sets in the refinement and if n is the minimum value for which this is true. If no such minimal n exists, the space is said to be of infinite covering dimension.

See also

• Compact space
• Paracompact space
• Normal space
• Realcompact space
• Pseudocompact space
• Mesocompact space
• Tychonoff space

References

• Watson, W. Stephen (1981). "Pseudocompact metacompact spaces are compact". Proc. Amer. Math. Soc. 81: 151–152 .
• Munkres, James (1999). Topology (2nd ed.). Prentice Hall. ISBN 0-13-181629-2. 
• Steen, Lynn Arthur; Seebach, J. Arthur Jr. (1995) [1978]. Counterexamples in Topology (Dover reprint of 1978 ed.). Berlin, New York: Springer-Verlag. ISBN 978-0-486-68735-3. MR507446  P.23.

This topology-related article is a stub. You can help Wikipedia by expanding it.v · Categories: Topology stubs Properties of topological spaces Compactness (mathematics) Wikimedia Foundation. 2010. Игры ⚽ Нужно сделать НИР? Tagbu World Snooker Championship 1993 Look at other dictionaries: space — 1. noun /speɪs/ a) The intervening contents of a volume. If it be only a Single Letter or two that drops, he thruſts the end of his Bodkin between every Letter of that Word, till he comes to a Space: and then perhaps by forcing thoſe Letters… …   Wiktionary Paracompact space — In mathematics, a paracompact space is a topological space in which every open cover admits a locally finite open refinement. Paracompact spaces are sometimes also required to be Hausdorff. Paracompact spaces were introduced by Dieudonné (1944).… …   Wikipedia Shrinking space — In mathematics, in the field of topology, a topological space is said to be a shrinking space if every open cover admits a shrinking. A shrinking of an open cover is another open cover indexed by the same indexing set, with the property that the… …   Wikipedia Orthocompact space — In mathematics, in the field of general topology, a topological space is said to be orthocompact if every open cover has an interior preserving open refinement. That is, given an open cover of the topological space, there is a refinement which is …   Wikipedia Compact space — Compactness redirects here. For the concept in first order logic, see compactness theorem. In mathematics, specifically general topology and metric topology, a compact space is an abstract mathematical space whose topology has the compactness… …   Wikipedia Moore space (topology) — In mathematics, more specifically point set topology, a Moore space is a developable regular Hausdorff space. Equivalently, a topological space X is a Moore space if the following conditions hold: Any two distinct points can be separated by… …   Wikipedia Dowker space — A Dowker space is a topological space that is T4 but not countably paracompact. Equivalences If X is a normal T1 space (a T4 space), then the following are equivalent: X is a Dowker space The product of X with the unit interval is not normal. C.… …   Wikipedia Pseudocompact space — In mathematics, in the field of topology, a topological space is said to be pseudocompact if its image under any continuous function to R is bounded.Conditions for pseudocompactness*Every countably compact space is pseudocompact. For normal… …   Wikipedia Mesocompact space — In mathematics, in the field of general topology, a topological space is said to be mesocompact if every open cover has a compact finite open refinement.[1] That is, given any open cover, we can find an open refinement with the property that… …   Wikipedia Point finite collection — In mathematics, a collection mathcal{U} of subsets of a topological space X is said to be point finite or a point finite collection if every point of X lies in only finitely many members of mathcal{U}. Compare this to the stronger property of… …   Wikipedia 18+ © Academic, 2000-2024 Contact us: Technical Support, Advertising Dictionaries export, created on PHP, Joomla, Drupal, WordPress, MODx. Mark and share Search through all dictionaries Translate… Search Internet Share the article and excerpts Direct link … Do a right-click on the link above and select “Copy Link”