The relations between the radicals of path algebras and connectivity of directed graphs are given. The relations between radicals of generalized matrix rings and Γrings are given. All the coquasitriangular structures of group algebra kG are found when G is a finitely generated abelian group. 2000 Mathematics subject Classification: 16w30, 05Cxx.

1.1. Baumslag's theorem has another facet. It shows that in the variety 2l of metabelian groups, every finitely generated $I-group G occurs as a subgroup of some finitely presented 2I-group G. The analogous result for the variety of all groups is a celebrated theorem of G. Higman [8] which states that a finitely generated group G is the subgroup of a finitely presented group G if, and only if, ...

A group $G$ has a finite special rank $r$ if every finitely generated subgroup of is by at most elements and there which exactly generators. If not such $r$, then we say that infinite rank. In this paper, study generalized radical non-abelian groups whose subgroups are transitively normal.

2 Arithmetic in an algebraic number field 30 2.1 Finitely generated abelian groups . . . . . . . . . . . . . . . . . . 30 2.2 The splitting field and the discriminant . . . . . . . . . . . . . . 31 2.3 Number fields . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 2.4 The ring of integers . . . . . . . . . . . . . . . . . . . . . . . . . . 39 2.5 Ideals . . . . . . . . . . . . . . ....

We construct for every graph product of finitely generated abelian groups a CAT(0) cubical complex on which it acts properly and cocompactly. The complex generalizes (up to subdivision) the Salvetti complex of a right-angled Artin group and the Coxeter complex of a right-angled Coxeter group.

We give the commensurability classifications of free products of finitely many finitely generated abelian groups. We show this coincides with the quasi-isometry classification and prove that this class of groups is quasiisometrically rigid. The following gives the complete commensurability and quasi-isometry classification of free products of finitely generated abelian groups. The quasi-isometr...