Words of Engel type are concise in residually finite groups

Abstract

Given a group-word [Formula: see text] and a group [Formula: see text], the verbal subgroup [Formula: see text] is the one generated by all [Formula: see text]-values in [Formula: see text]. The word [Formula: see text] is said to be concise if [Formula: see text] is finite whenever the set of [Formula: see text]-values in [Formula: see text] is finite. In 1960s, Hall asked whether every word is concise but later Ivanov answered this question in the negative. On the other hand, Hall’s question remains wide open in the class of residually finite groups. In the present paper we show that various generalizations of the Engel word are concise in residually finite groups.