A class of angelic sequential non-Fréchet-Urysohn topological groups |
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Authors: | MJ Chasco E Martín-Peinador V Tarieladze |
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Institution: | a Departamento de Física y Matemática Aplicada, Universidad de Navarra, Spain b Departamento de Geometría y Topología, Universidad Complutense, Spain c Niko Muskhelishvili Institute of Computational Mathematics, Georgia |
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Abstract: | Fréchet-Urysohn (briefly F-U) property for topological spaces is known to be highly non-multiplicative; for instance, the square of a compact F-U space is not in general Fréchet-Urysohn P. Simon, A compact Fréchet space whose square is not Fréchet, Comment. Math. Univ. Carolin. 21 (1980) 749-753. 27]]. Van Douwen proved that the product of a metrizable space by a Fréchet-Urysohn space may not be (even) sequential. If the second factor is a topological group this behaviour improves significantly: we have obtained (Theorem 1.6(c)) that the product of a first countable space by a F-U topological group is a F-U space. We draw some important consequences by interacting this fact with Pontryagin duality theory. The main results are the following:- (1)
- If the dual group of a metrizable Abelian group is F-U, then it must be metrizable and locally compact.
- (2)
- Leaning on (1) we point out a big class of hemicompact sequential non-Fréchet-Urysohn groups, namely: the dual groups of metrizable separable locally quasi-convex non-locally precompact groups. The members of this class are furthermore complete, strictly angelic and locally quasi-convex.
- (3)
- Similar results are also obtained in the framework of locally convex spaces.
Another class of sequential non-Fréchet-Urysohn complete topological Abelian groups very different from ours is given in E.G. Zelenyuk, I.V. Protasov, Topologies of Abelian groups, Math. USSR Izv. 37 (2) (1991) 445-460. 32]]. |
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Keywords: | primary 22A05 secondary 46A16 |
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