| Título: | Basic topological properties of Fox's branched coverings. |
| Autores: | Montesinos Amilibia, José María |
| Tipo de documento: | texto impreso |
| Editorial: | Editorial Complutense, 2004 |
| Palabras clave: | Estado = Publicado , Materia = Ciencias: Matemáticas , Tipo = Sección de libro |
| Resumen: |
Motivated by applications to open manifolds and wild knots, the author in this article revisits R. H. Fox's theory [in A symposium in honor of S. Lefschetz, 243–257, Princeton Univ. Press, Princeton, N.J., 1957; MR0123298 (23 #A626)] of singular covering spaces. Central to this theory is the notion of spread: a continuous map between T1-spaces such that the connected components of inverse images of open subsets of the target space form a basis for the topology of the source space. The fiber of a spread is shown to embed into an inverse limit of discrete spaces. If this embedding is actually surjective for all fibers, then the spread is called complete. Every spread admits a unique completion up to homeomorphism. This understood, a ramified covering f:Y?Z is a complete spread between connected spaces whose set of ordinary points, and its preimage, are dense and locally connected in Z, respectively Y. Moreover, f is the completion of its associated unramified covering, which in fact determines it uniquely. The interpretation of spreads via inverse limits is used by the author to show that a ramified covering f:Y?Z is surjective and open if Z satisfies the first countability axiom, and that it is discrete if all the ramification indices are finite. An interesting example is constructed of a ramified covering of infinite degree of the 3-sphere branched over a wild knot and having a compact but non-discrete fiber. A few intriguing open problems end the article: Are there non-surjective or non-open ramified coverings? Is there a ramified covering with a fiber homeomorphic to the Cantor set? |
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