Topology and its Applications ( IF 0.6 ) Pub Date : 2021-06-25 , DOI: 10.1016/j.topol.2021.107761 Edgar Márquez Rodríguez , Mikhail Tkachenko
A topological group G with is called d-independent if for every subgroup S of G with , one can find a countable dense subgroup H of G such that . Therefore, d-independent groups are separable and have cardinality at least . Our main result is a purely algebraic characterization of d-independence in the class of compact metrizable abelian groups. We prove that a compact metrizable abelian group G with is d-independent if and only if for every integer , either or . This characterization implies that a compact metrizable abelian group is d-independent if and only if it is maximally fragmentable [Comfort and Dikranjan (2014) [4]] iff G an M-group as defined by Dikranjan and Shakhmatov (2016) in [7].
Also we present a characterization of separable metrizable d-independent abelian groups and show that products of separable topological groups can often be d-independent, even if the factors fail to be d-independent.
中文翻译:
D-独立拓扑群
甲拓扑群G ^与被称为d无关,若对所有子群小号的ģ与,可以发现一个可数稠密子群ħ的ģ使得. 因此,在独立团是可分离的,并至少有基数. 我们的主要结果是对紧凑可度量阿贝尔群类中d独立性的纯代数表征。我们证明了一个紧度量阿贝尔群G ^与与d无关当且仅当对于每个整数, 任何一个 或者 . 这种表征意味着一个紧凑的可计量阿贝尔群是d独立的,当且仅当它是最大可碎片化的[Comfort and Dikranjan (2014) [4]] iff G是由 Dikranjan 和 Shakhmatov (2016) 在 [7 ]中定义的M 群]。
此外,我们还介绍了可分离的可计量d独立阿贝尔群的表征,并表明可分离拓扑群的乘积通常可以是d独立的,即使这些因子不能是d独立的。