Weak Hausdorff space
topological spaces | |
---|---|
Kolmogorov classification | |
T0 | (Kolmogorov) |
T1 | (Fréchet) |
T2 | (Hausdorff) |
T2½ | (Urysohn) |
completely T2 | (completely Hausdorff) |
T3 | (regular Hausdorff) |
T3½ | (Tychonoff) |
T4 | (normal Hausdorff) |
T5 | (completely normal Hausdorff) |
T6 | (perfectly normal Hausdorff) |
In
The notion was introduced by M. C. McCord[4] to remedy an inconvenience of working with the category of Hausdorff spaces. It is often used in tandem with compactly generated spaces in algebraic topology. For that, see the category of compactly generated weak Hausdorff spaces.
k-Hausdorff spaces
A k-Hausdorff space[5] is a topological space which satisfies any of the following equivalent conditions:
- Each compact subspace is Hausdorff.
- The diagonal is k-closedin
- A subset is k-closed, if is closed in for each compact
- Each compact subspace is closed and strongly locally compact.
- A space is strongly locally compact if for each and each (not necessarily open) neighborhoodof there exists a compact neighborhood of such that
- A space is strongly locally compact if for each and each (not necessarily open)
Properties
- A k-Hausdorff space is weak Hausdorff. For if is k-Hausdorff and is a continuous map from a compact space then is compact, hence Hausdorff, hence closed.
- A Hausdorff space is k-Hausdorff. For a space is Hausdorff if and only if the diagonal is closed in and each closed subset is a k-closed set.
- A k-Hausdorff space is KC. A KC space is a topological space in which every compact subspace is closed.
- To show that the coherent topology induced by compact Hausdorff subspaces preserves the compact Hausdorff subspaces and their subspace topology requires that the space be k-Hausdorff; weak Hausdorff is not enough. Hence k-Hausdorff can be seen as the more fundamental definition.
Δ-Hausdorff spaces
A Δ-Hausdorff space is a topological space where the image of every path is closed; that is, if whenever is continuous then is closed in Every weak Hausdorff space is -Hausdorff, and every -Hausdorff space is a T1 space. A space is Δ-generated if its topology is the finest topology such that each map from a topological -simplex to is continuous. -Hausdorff spaces are to -generated spaces as weak Hausdorff spaces are to compactly generated spaces.
See also
- Fixed-point space – Space where all functions have fixed points, a Hausdorff space where every continuous function from the space into itself has a fixed point.
- Hausdorff space – Type of topological space
- Locally Hausdorff space
- Particular point topology
- Quasitopological space – a set X equipped with a function that associates to every compact Hausdorff space K a collection of maps K→C satisfying certain natural conditions
- Separation axiom – Axioms in topology defining notions of "separation"
References
- MR 0547371.
- ISBN 0-226-51183-9(See chapter 5)
- ^ Strickland, Neil P. (2009). "The category of CGWH spaces" (PDF).
- MR 0251719.
- .