The free topological group over the rationals (original) (raw)

1979, General Topology and its Applications

In this paper we investigate the topological structure of the Graev free topoiogical group over ;he rationals. We show that this free group fails to be a k-space and fails to carry the weak topology generalied by its subspaces of words of length less than or equal to n. As tools in this investigation we establish some properties of net convergence in free groups and also some propertics of certain canonical maps which are closely related to the topological structure of free groups. j A,M.S. (M(X) Subj. Class.: 22A99,20E05, 55D50,55620.

Free k-groups and free topological groups

General Topology and its Applications, 1975

This is the first of two papers which will explore analogues iCl the category of "compactly generated" groups of free topological groups and free products of topological groups, considered as constructions in the category of all topological groups. In particular, this pnp~ contains an existence th;eorem for free k-groups and a new existence theorem for free topological groups which is rather more constructive than previous p:oofs, i.md r:mploys the theory of k-spaces (hence, compactness argtiments) rather than the norms [ 71, pseudometrics [ 33, unitat-y groups [41/ or other machinery previously used.

The character of free topological groups II

Applied General Topology, 2005

A systematic analysis is made of the character of the free and free abelian topological groups on metrizable spaces and compact spaces, and on certain other closely related spaces. In the first case, it is shown that the characters of the free and the free abelian topological groups on X are both equal to the "small cardinal" d if X is compact and metrizable, but also, more generally, if X is a non-discrete k!-space all of whose compact subsets are metrizable, or if X is a non-discrete Polish space. An example is given of a zero-dimensional separable metric space for which both characters are equal to the cardinal of the continuum. In the case of a compact space X, an explicit formula is derived for the character of the free topological group on X involving no cardinal invariant of X other than its weight; in particular the character is fully determined by the weight in the compact case. This paper is a sequel to a paper by the same authors in which the characters of the free groups were analysed under less restrictive topological assumptions.

The character of free topological groups I

Applied General Topology, 2005

A systematic analysis is made of the character of the free and free abelian topological groups on uniform spaces and on topological spaces. In the case of the free abelian topological group on a uniform space, expressions are given for the character in terms of simple cardinal invariants of the family of uniformly continuous pseudometrics of the given uniform space and of the uniformity itself. From these results, others follow on the basis of various topological assumptions. Amongst these: (i) if X is a compact Hausdorff space, then the character of the free abelian topological group on X lies between w(X) and w(X) ℵ 0 , where w(X) denotes the weight of X; (ii) if the Tychonoff space X is not a P-space, then the character of the free abelian topological group is bounded below by the "small cardinal" d; and (iii) if X is an infinite compact metrizable space, then the character is precisely d. In the non-abelian case, we show that the character of the free abelian topological group is always less than or equal to that of the corresponding free topological group, but the inequality is in general strict. It is also shown that the characters of the free abelian and the free topological groups are equal whenever the given uniform space is ω-narrow. A sequel to this paper analyses more closely the cases of the free and free abelian topological groups on compact Hausdorff spaces and metrizable spaces.

On the topology of free paratopological groups

Bulletin of the London Mathematical Society, 2012

The result often known as Joiner's lemma is fundamental in understanding the topology of the free topological group F (X) on a Tychonoff space X. In this paper, an analogue of Joiner's lemma for the free paratopological group FP (X) on a T 1 space X is proved. Using this, it is shown that the following conditions are equivalent for a space X: (1) X is T 1 ; (2) FP (X) is T 1 ; (3) the subspace X of FP (X) is closed; (4) the subspace X −1 of FP (X) is discrete; (5) the subspace X −1 is T 1 ; (6) the subspace X −1 is closed; and (7) the subspace FP n (X) is closed for all n ∈ N, where FP n (X) denotes the subspace of FP (X) consisting of all words of length at most n.

A remark on free topological groups with no small subgroups

Journal of the Australian Mathematical Society, 1974

For a completely regular space X let G(X) be the Graev free topological group on X. While proving G(X) exists for completely regular spaces X, Graev showed that every pseudo-metric on X can be extended to a two-sided invariant pseudo-metric on the abstract group G(X). The free group topology on G(X) is usually strictly finer than this pseudo-metric topology. In particular this is the case when X is not totally disconnected (see Morris and Thompson [7]). It is of interest to know when G(X) has no small subgroups (see Morris [5]). Morris and Thompson [6] showed that this is the case if and only if X admits a continuous metric. The proof relied on properties of the free group topology and it is natural to ask if G(X) with its pseudo-metric topology has no small subgroups when and only when X admits a continuous metric. We show that this is the case. Topological properties of G(X) associated with the pseudo-metric topology have recently been studied by Joiner [3] and Abels [1].

On the topology of free paratopological groups. II

Topology and its Applications, 2013

Let FP (X) be the free paratopological group on a topological space X. For n ∈ N, denote by FP n (X) the subset of FP (X) consisting of all words of reduced length at most n, and by i n the natural mapping from (X ⊕ X −1 ⊕ {e}) n to FP n (X). In this paper a neighbourhood base at the identity e in FP 2 (X) is found. A number of characterisations are then given of the circumstances under which i 2 : (X ⊕ X −1 d ⊕ {e}) 2 → FP 2 (X) is a quotient map, where X is a T 1 space and X −1 d denotes the set X −1 equipped with the discrete topology. Further characterisations are given in the case where X is a transitive T 1 space. Several specific spaces and classes of spaces are also examined. For example, i 2 is a quotient for every countable subspace of R, i 2 is not a quotient for any uncountable compact subspace of R, and it is undecidable in ZFC whether an uncountable subspace of R exists for which i 2 is a quotient.

Free topological groups over metrizable spaces

Topology and its Applications, 1989

Let X be a metrizable space and F(X) and A(X) be the free topological group over X and the free Abelian topological group over X respectively. We establish the following criteria:

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