soluble group 20E34 2 20D10 1 20D15 1 20D20 1 20E15 1 20F16; Secondary 20E25 1 20F19,20F22 1 20F22 1 20F50 1 Primary 20E15 1 \(\cal F\) -critical group,\(\cal F\) -maximal subgroup 1 \(\cal F\)-hypercentre 1 abnormal subgroups 1 boundary condition 1 contranormal subgroup 1 finite special rank 1 hereditary formation 1 locally graded group 1 locally nilpotent radical 1 locally nilpotent residual 1 nilpotent group 1 normal subgroups 1 periodic group 1 permutable subgroups 1 pronormal subgroups 1 radical group 1 saturated formation 1 subnormal subgroup 1 supersolublegroup 1