topological invariant subgroup

例句：

1. 1.The topological invariant subgroup of a group is the set of all elements that are invariant under the group's action.
   一个群的拓扑不变子群是所有在群作用下不变的元素的集合。
2. 2.In topology, an open subset is a topological invariant subgroup.
   在拓扑学中，开集是一个拓扑不变子群。
3. 3. The study of topological invariant subgroups is important in understanding the structure of groups.
   研究拓扑不变子群对于理解群的结构非常重要。