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Automorphisms of divisible rigid groupsD. Ovchinnikov
A group G is said to be rigid if it has a normal series
\[G=G_1>G_2>\ldots >G_n>G_{n+1}=1\]
in which each factor \(G_i/G_{i+1}\) is an abelian group that is torsion
free as a \(\mathbb{Z}[G/G_i]\)-module. Rigid groups are introduced in [1] in connection with algebraic geometry over groups.
Important examples of rigid groups are free solvable groups. \(G\) is divisible [2] if
all \(G_i/G_{i+1}\) are divisible modules. Any \(\mathbb{Z}[G/G_i]\) is a (right) Ore domain, and we denote
by \(Q(G_i/G_{i+1})\) the (right) Ore skew field of fractions of \(\mathbb{Z}[G/G_i]\). Therefore, for a divisible rigid group \(G\),
the quotient \(G_i/G_{i+1}\) can be viewed as a vector space over \(Q(G_i/G_{i+1})\). \(G\) is splittable if it splits into a
semidirect product \(A_1A_2\ldots A_n\) of abelian groups \(A_i\cong G_i/G_{i+1}\). A splittable divisible rigid group is uniquely defined by
the dimensions of \(A_i\) over \(Q_i=Q(A_1\ldots A_{i-1})\) (denoted by \(\alpha_i\)). It is proved that every divisible
rigid group is splittable [3] and any rigid group is embedable into some divisible rigid group [2].
References
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