20E34 3 20F16; Secondary 20E25 3 20F22 3 20F50 3 Primary 20E15 finite special rank 2 locally nilpotent radical 2 locally nilpotent residual 2 periodic group 2 soluble group 2 transitively normal subgroups 2 dense family of subgroups 1 finite central dimension 1 infinite dimensional linear group 1 infinite group 1 linear group 1 locally soluble group 1