a1 Mathematisches Institut Am Hubland 12 D-W-8700 Würzburg Germany
a2 Dipartimento Di Matematica Piazza di Porta San Donato, 5 I-40127 Bologna Italy
Let G be a group and let ℓ(G) be the set of all conjugacy classes [H] of subgroups H of G, where a partial order ≤ is defined by [H1] ≤ [H2] if and only if H1, is contained in some conjugate of H2.
A number of papers (see for example  and the references mentioned there) deal with the question of characterizing groups G by the poset ℓ(G). For example, in  it was shown that if ℓ(G) and ℓ(H) are order-isomorphic and G is a noncyclic p-group then |G| = |H|. Moreover, if G is abelian, then G = H, and if G is metacyclic then H is metacyclic.
(Received April 23 1992)
p1 Work supported by M.U.R.S.T. of Itay.