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Außenhofer, Lydia and Dikranjan, Dikran and Martín Peinador, Elena
(2015)
*Locally Quasi-Convex Compatible Topologies on a Topological Group.*
Axioms, 4
(4).
pp. 436-458.
ISSN 2075-1680

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Official URL: https://doi.org/10.3390/axioms4040436

## Abstract

For a locally quasi-convex topological abelian group (G, τ), we study the poset C (G, τ) of all locally quasi-convex topologies on G that are compatible with τ (i.e., have the same dual as (G, τ)) ordered by inclusion. Obviously, this poset has always a bottom element, namely the weak topology σ(G, Gb). Whether it has also a top element is an open question. We study both quantitative aspects of this poset (its size) and its qualitative aspects, e.g., its chains and anti-chains. Since we are mostly interested in estimates “from below”, our strategy consists of finding appropriate subgroups H of G that are easier to handle and show that C (H) and C (G/H) are large and embed, as a poset, in C (G, τ). Important special results are: (i) if K is a compact subgroup of a locally quasi-convex group G, then C (G) and C (G/K) are quasi-isomorphic (3.15); (ii) if D is a discrete abelian group of infinite rank, then C (D) is quasi-isomorphic to the poset FD of filters on D (4.5). Combining both results, we prove that for an LCA (locally compact abelian) group G with an open subgroup of infinite co-rank (this class includes, among others, all non-σ-compact LCA groups), the poset C (G) is as big as the underlying topological structure of (G, τ) (and set theory) allows. For a metrizable connected compact group X, the group of null sequences G = c0(X) with the topology of uniform convergence is studied. We prove that C (G) is quasi-isomorphic to P(R) (6.9).

Item Type: | Article |
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Uncontrolled Keywords: | locally quasi-convex topology; compatible topology; quasi-convex sequence; quasi-isomorphic posets; free filters; Mackey groups |

Palabras clave (otros idiomas): | Topología algebraica |

Subjects: | Sciences > Mathematics Sciences > Mathematics > Algebraic geometry Sciences > Mathematics > Topology |

ID Code: | 63184 |

Deposited On: | 27 Nov 2020 12:33 |

Last Modified: | 27 Nov 2020 13:05 |

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