Automorphisms of a free group of infinite rank

The problem of classifying the automorphisms of a free group of infinite countable rank is investigated. Quite a reasonable generating set for the group $\mathrm{Aut}F_{\infty}$ is described. Some new subgroups of this group and structural results for them are presented. The main result says that the group of all automorphisms is generated (modulo the $IA$-automorphisms) by strings and lower triangular automorphisms.