Lie methods for countably categorical Engel groups: the Wilson conjecture for $4$-Engel $5$-groups

Abstract

We are interested in the following conjecture of Wilson from 1981: every locally nilpotent countably categorical group is nilpotent. Following our previous work on the Lie algebra analogue of the conjecture, we use Lie methods to deduce the first nontrivial cases of the Wilson conjecture for n-Engel groups: countably categorical 3-Engel groups and 4-Engel 5-groups are nilpotent, from which we also conclude that countably categorical 4-Engel groups of odd exponent are nilpotent. This is implemented via an exceptional case of the Lazard correspondence, checked using computer algebra systems. We also study the transfer of nilpotency results between the three categories: groups, Lie algebras, associative algebras. Among other things, we prove that the Wilson conjecture implies the analogous nilpotency statement for associative algebras (modulo the commutative case).