Abstract:We prove that a Hausdorff paratopological group G is meager if and only if there are a nowhere dense subset A ⊂ G and a countable set C ⊂ G such that CA = G = AC.2010 MSC: 22A05, 22A30.
“…Using this combinatorial characterization and the tree technique from [10], we can prove that the ideal of scattered subsets of a countable group G is coanalytic in P G . [17], every meager topological group G can be represented as the product G = CN of some countable subset C and nowhere dense subset N . Every infinite group G can be represented as a union of some countable family of small subsets [3].…”
Section: Comments and Open Questionsmentioning
confidence: 99%
“…4. By [17], every meager topological group G can be represented as the product G = CN of some countable subset C and nowhere dense subset N . Every infinite group G can be represented as a union of some countable family of small subsets [3].…”
We explore the Borel complexity of some basic families of subsets of a countable group (large, small, thin, sparse and other) defined by the size of their elements. Applying the obtained results to the Stone-Čech compactification βG of G, we prove, in particular, that the closure of the minimal ideal of βG is of type F σδ .
“…Using this combinatorial characterization and the tree technique from [10], we can prove that the ideal of scattered subsets of a countable group G is coanalytic in P G . [17], every meager topological group G can be represented as the product G = CN of some countable subset C and nowhere dense subset N . Every infinite group G can be represented as a union of some countable family of small subsets [3].…”
Section: Comments and Open Questionsmentioning
confidence: 99%
“…4. By [17], every meager topological group G can be represented as the product G = CN of some countable subset C and nowhere dense subset N . Every infinite group G can be represented as a union of some countable family of small subsets [3].…”
We explore the Borel complexity of some basic families of subsets of a countable group (large, small, thin, sparse and other) defined by the size of their elements. Applying the obtained results to the Stone-Čech compactification βG of G, we prove, in particular, that the closure of the minimal ideal of βG is of type F σδ .
“…x → x −1 , is also continuous. The the properties of topological groups have been widely used in the study of topology, analysis and category, see [1,2,4,27,28,29,30,31,32,38,39]. For more details about topological groups, the reader see [3].…”
In this paper, we pose the concepts of pre-topological groups and some generalizations of pre-topological groups. First, we systematically investigate some basic properties of pre-topological groups; in particular, we prove that each T 0 pre-topological group is regular and every almost topological group is completely regular which extends A.A. Markov's theorem to the class of almost topological groups. Moreover, it is shown that an almost topological group is τ -narrow if and only if it can be embedded as a subgroup of a pre-topological product of almost topological groups of weight less than or equal to τ . Finally, the cardinal invariant, the precompactness and the resolvability are investigated in the class of pre-topological groups.
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