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Published online by Cambridge University Press: 24 October 2008
Let be the class of groups possessing a subgroup of index n for each divisor n of the group order. McLain (7) initiated the formal investigation of
and observed that every solvable group is a direct factor of an
-group. However, subclasses of
provide some interesting problems. Various subclasses of
which satisfy other properties were studied by McLain; the upshot being that these classes approach supersolvability. This program was pursued by Humphreys (3) and Humphreys and Johnson (4), among others. In particular,
, the largest quotient closed subclass of
, was considered in (3) and (4). Humphreys (3) has shown an odd order
-group is supersolvable, but provides some non-supersolvable
groups. Our motivation is that if S ∈ QR0(S3), the formation generated by S3, and V is a faithful irreducible GF(2) [S]-module, the semidirect product VS ∈
.