Uncountable extended residually finite groups
摘要
A subgroup X of a group G is closed in the profinite topology if it can be obtained as intersection of a collection of subgroups of finite index of G, and a group G is said to be an ERF-group if all its subgroups are closed. It is proved here that if all large subgroups of an uncountable group G are closed, then G is an ERF-group, provided that either G is nilpotent-by-finite or it has finite conjugacy classes. Moreover, uncountable groups in which every large proper subgroup is an ERF-group are considered.