Complemented group

Article summary

In mathematics, in the realm of group theory, the term complemented group is used in two distinct, but similar ways. In , a complemented group is one in which every subgroup has a group-theoretic complement. Such groups are called completely factorizable groups in the Russian literature, following and . The following are equivalent for any finite group G: * G is complemented * G is a subgroup of a direct product of groups of square-free order (a special type of Z-group) * G is a supersolvable group with elementary abelian Sylow subgroups (a special type of A-group), . Later, in , a group is said to be complemented if the lattice of subgroups is a complemented lattice, that is, if for every subgroup H there is a subgroup K such that H ∩ K = 1 and ⟨H, K ⟩ is the whole group. Hall's definition required in addition that H and K permute, that is, that HK = {hk : h in H, k in K} form a subgroup. Such groups are also called K-groups in the Italian and lattice theoretic literature, such as . The Frattini subgroup of a K-group is trivial; if a group has a core-free maximal subgroup that is a K-group, then it itself is a K-group; hence subgroups of K-groups need not be K-groups, but quotient groups and direct products of K-groups are K-groups, . In it is shown that every finite simple group is a complemented group.…

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