characterization of compactly generated space
We give equivalent conditions when a Hausdorff topological space is compactly generated. First we need a definition.
Definition. Let be a space and a topological space. We define to be the set of functions such that for every compact
, closed set
the restriction
is continuous
.
Clearly, for such spaces . With this we have the following theorem.
Theorem. Let be a Hausdorff space. Then the following conditions are equivalent.
i) is compactly generated
ii) carries the final topology generated by the family of inclusion mappings .
iii) For every topological space we have .
iv) is an image of a locally compact space under a quotient mapping.
Remark.It follows easily from this that if there is a quotient mapping which maps a compactly generated space onto a Hausdorff space then is compactly generated.