locally finite group 1 20E15 1 20F16 1 20F18 1 20F19 1 20F50 1 \(\mathrm{GNA}\)-subgroup 1 abnormal subgroup 1 condition of normality 1 decomposable abelian subgroup 1 group 1 involution 1 locally nilpotent residual 1 minimal condition 1 non-periodic group 1 normal subgroup 1 order of the group 1 pronormal subgroup 1 self-normalizing subgroup 1 subgroup 1