20F16 2 20F18 2 20F19 2 abnormal subgroup normal subgroup 2 pronormal subgroup 2 self-normalizing subgroup 2 (generalized) radical group 1 20E15 1 20F22 1 20F50 1 \(GNA\)-subgroup 1 \(\mathrm{GNA}\)-subgroup 1 locally finite group 1 locally finite radical 1 locally nilpotent radical 1 locally nilpotent residual 1