NEW TWO-RADII THEOREMS IN THE THEORY OF HARMONIC FUNCTIONS
Vitalii Vladimirovich Volchkov · Izvestiya Mathematics · 1995
The aim of this paper is to describe the structure of finitely generated subgroups of a family of branch groups containing the first Grigorchuk group and the Gupta-Sidki 3-group.We then use this to show that all the groups in this family are subgroup separable (LERF).These results are obtained as a corollary of a more general structural statement on subdirect products of just infinite groups.