Abstract:
An abelian group AA is called ππ-bounded for a set of prime numbers ππ, if all pp-primary components tp(A/B)tp(A/B) are finite for every subgroup B⊂AB⊂A and for every p∈πp∈π. E. V. Sokolov has introduced the class of ππ-bounded groups investigating FπFπ-separable and π′-isolated subgroups in the general group theory. The description of torsion π-bounded groups is trivial. E. V. Sokolov has proved that the description of mixed π-bounded groups can be reduced to the case of torsion free groups.
We consider the class of π-bounded torsion free groups in the present paper and we prove that this class of groups coincides with the class of π-local torsion free abelian groups of finite rank. We consider also abelian groups satisfying the condition (∗), that is such groups that their quotient groups don't contain subgroups of the form Zp∞ for all prime numbers p∈π, where π is a fixed set of prime numbers. It is clear that all π-bounded groups satisfy the condition (∗). We prove that an abelian group A satisfies the condition (∗) if and only if both groups t(A) and A/t(A) satisfy the condition (∗). We construct also an example of a non-splitting mixed group of rank 1, satisfying the condition (∗), for every infinite set π of prime numbers.