The Sylow graph Γ(G) of a finite group G originated from recent
investigations on the so--called N--closed classes of groups. The
connectivity of Γ(G) was proved only few years ago, involving the
classification of finite simple groups, and the structure of G may be
strongly restricted, once information on Γ(G) are given. The first
result of the present paper deals with a condition on N--closed
classes of groups. The second result deals with a computational criterion,
related to the connectivity of Γ(G).Comment: 8 pp. with Appendix; Fundamental revisions have been don