Sr. Li, F-SUBNORMAL AND F-SUBABNORMAL CHAINS IN FINITE-GROUPS, Science in China. Series A, Mathematics, Physics, Astronomy & Technological Sciences, 41(11), 1998, pp. 1121-1127
The class F-pc of all finite groups G is defined such that X less than
or equal to G implies that there exists an F-subnormal subgroup S of
G containing X such that X is F-subabnormal in S, where F is a saturat
ed formation, closed under taken subgroups. Groups in F-pc are charact
erized by F-projectors and F-covering subgroups.