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The impact of the Bohr topology on selective pseudocompactness

机译:玻尔拓扑对选择性拟紧凑性的影响

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Recall that a space X is selectively pseudocompact if for every sequence {U-n : n is an element of N} of non-empty open subsets of X one can choose a point x(n) is an element of U-n for all n is an element of N such that the resulting sequence {x(n) : n is an element of N} has an accumulation point in X. This notion was introduced under the name strong pseudocompactness by Garcia-Ferreira and Ortiz-Castillo; the present name is due to Dorantes-Aldama and the first listed author. In 2015, Garcia-Ferreira and Tomita constructed a pseudocompact Boolean group that is not selectively pseudocompact. We prove that if the subgroup topology on every countable subgroup H of an infinite Boolean topological group G is finer than its maximal precompact topology (the so-called Bohr topology of H), then G is not selectively pseudocompact, and from this result we deduce that many known examples in the literature of pseudocompact Boolean groups automatically fail to be selectively pseudocompact. We also show that, under the Singular Cardinal Hypothesis, every infinite pseudocompact Boolean group admits a pseudocompact reflexive group topology which is not selectively pseudocompact. (C) 2019 Elsevier B.V. All rights reserved.
机译:回想一下,如果对于每个序列{Un:n是N的元素}的X的非空开放子集,可以选择一个点x(n)是Un的元素,因为所有n是一个元素,那么空间X是选择性伪紧致的N使得生成的序列{x(n):n是N的元素)在X中具有累加点。这个概念由Garcia-Ferreira和Ortiz-Castillo以强伪紧凑性的名称引入;现在的名字是由Dorantes-Aldama和第一位列出的作者给定的。在2015年,加西亚·费雷拉(Garcia-Ferreira)和富田(Tomita)构造了一个非伪压缩布尔假组。我们证明,如果无限布尔拓扑组G的每个可数子组H上的子组拓扑都比其最大预紧拓扑(H的所谓玻尔拓扑)更精细,则G并非选择性地伪紧致,并且从这个结果我们可以得出伪紧凑布尔组文献中的许多已知示例自动无法选择性地伪紧凑。我们还表明,在奇异基数假设下,每个无限的伪紧凑布尔组都接受一个伪紧凑自反组拓扑,该拓扑不是选择性伪紧凑的。 (C)2019 Elsevier B.V.保留所有权利。

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