Constructing free groups in a normal subgroup of the multiplicative group of division rings. (Q500218)

Let \(D\) be a division ring and \(N\) be a normal subgroup of the multiplicative group \(D^*\) of \(D\). From previous results of Lichtman it follows that if \(N\) contains a nonabelian torsion-free polycyclic-by-finite subgroup \(G\) then \(N\) contains a free noncyclic subgroup. In the article under review, the author provides some method to construct this free subgroup of \(N\) in terms of elements of \(G\).