Convention:Hausdorffness assumption: Difference between revisions

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==For separation axioms==
==For separation axioms==


In the Topospaces wiki, we follow the convention that Hausdorffness is assumed for all ''higher'' separation axioms. In particular, [[normal space]]s and [[regular space]]s are ''assumed'' to have the Hausdorffness condition. This convention is compatible with a number of general-purpose textbooks in point-set topology and algebraic topology, including those by Munkres, Singer-Thorpe, Hatcher, among others.
We do ''not'' assume [[normal space]]s or [[regular space]]s to satisfy the T1 or Hausdorff conditions. ''Note'': Earlier we did make that assumption, so some content is outdated and not synced with the latest assumptions.
 
People working in point-set topology research sometimes do ''not'' assume the Hausdorffness condition for normal spaces, so please keep this in mind.


==For compactness axioms==
==For compactness axioms==

Latest revision as of 17:53, 27 January 2012

This article is about a convention that is followed in this wiki. The aim is that every page on the wiki follows this convention unless explicitly stated otherwise on the page; however, in practice, this may not have been implemented

For separation axioms

We do not assume normal spaces or regular spaces to satisfy the T1 or Hausdorff conditions. Note: Earlier we did make that assumption, so some content is outdated and not synced with the latest assumptions.

For compactness axioms

For compactness-type properties, we do not assume Hausdorffness. Thus, a compact space need not be Hausdorff. This convention is again in line with a number of general-purpose textbooks in point-set topology, but is not in line with terminology in algebraic geometry, which often follows the Bourbaki convention of calling a compact non-Hausdorff space quasi-compact.

For manifolds

We assume manifolds to be Hausdorff. This convention is again in line with most treatises on point-set topology, algebraic topology, and differential topology. The non-Hausdorff versions are called locally Euclidean spaces here.