Locally nilpotent normal subgroup

Definition
A subgroup of a group is termed a locally nilpotent normal subgroup if it is locally nilpotent as a group, and normal as a subgroup.

Facts

 * The subgroup generated by all locally nilpotent normal subgroups is the unique largest locally nilpotent normal subgroup of the group, and is termed the Hirsch-Plotkin radical of the group.