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A note on paratopological groups

Chuan Liu (2006)

Commentationes Mathematicae Universitatis Carolinae

In this paper, it is proved that a first-countable paratopological group has a regular G δ -diagonal, which gives an affirmative answer to Arhangel’skii and Burke’s question [Spaces with a regular G δ -diagonal, Topology Appl. 153 (2006), 1917–1929]. If G is a symmetrizable paratopological group, then G is a developable space. We also discuss copies of S ω and of S 2 in paratopological groups and generalize some Nyikos [Metrizability and the Fréchet-Urysohn property in topological groups, Proc. Amer. Math....

A note on pseudobounded paratopological groups

Fucai Lin, Shou Lin, Iván Sánchez (2014)

Topological Algebra and its Applications

Let G be a paratopological group. Then G is said to be pseudobounded (resp. ω-pseudobounded) if for every neighbourhood V of the identity e in G, there exists a natural number n such that G = Vn (resp.we have G = ∪ n∈N Vn). We show that every feebly compact (2-pseudocompact) pseudobounded (ω-pseudobounded) premeager paratopological group is a topological group. Also,we prove that if G is a totally ω-pseudobounded paratopological group such that G is a Lusin space, then is G a topological group....

A note on the structure of quadratic Julia sets

Karsten Keller (1997)

Commentationes Mathematicae Universitatis Carolinae

In a series of papers, Bandt and the author have given a symbolic and topological description of locally connected quadratic Julia sets by use of special closed equivalence relations on the circle called Julia equivalences. These equivalence relations reflect the landing behaviour of external rays in the case of local connectivity, and do not apply completely if a Julia set is connected but fails to be locally connected. However, rational external rays land also in the general case. The present...

A note on topological groups and their remainders

Liang-Xue Peng, Yu-Feng He (2012)

Czechoslovak Mathematical Journal

In this note we first give a summary that on property of a remainder of a non-locally compact topological group G in a compactification b G makes the remainder and the topological group G all separable and metrizable. If a non-locally compact topological group G has a compactification b G such that the remainder b G G of G belongs to 𝒫 , then G and b G G are separable and metrizable, where 𝒫 is a class of spaces which satisfies the following conditions: (1) if X 𝒫 , then every compact subset of the space X is a...

A note on Tsirelson type ideals

Boban Veličković (1999)

Fundamenta Mathematicae

Using Tsirelson’s well-known example of a Banach space which does not contain a copy of c 0 or l p , for p ≥ 1, we construct a simple Borel ideal I T such that the Borel cardinalities of the quotient spaces P ( ) / I T and P ( ) / I 0 are incomparable, where I 0 is the summable ideal of all sets A ⊆ ℕ such that n A 1 / ( n + 1 ) < . This disproves a “trichotomy” conjecture for Borel ideals proposed by Kechris and Mazur.

A note on universal minimal dynamical systems

Sławomir Turek (1991)

Commentationes Mathematicae Universitatis Carolinae

Let M ( G ) denote the phase space of the universal minimal dynamical system for a group G . Our aim is to show that M ( G ) is homeomorphic to the absolute of D 2 ω , whenever G is a countable Abelian group.

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