Groups with cofinite Zariski topology and potential density

Abstract

Tkachenko and Yaschenko [34] characterized the abelian groups G such that all proper unconditionally closed subsets of G are finite, these are precisely the abelian groups G having cofinite Zariski topology (they proved that such a G is either almost torsion-free or of prime exponent). The authors connected this fact to Markov's notion of potential density and the existence of pairs of independent group topologies. Inspired by their work, we examine the class C of groups having cofinite Zariski topology in the general case, obtaining a number of very strong restrictions on these groups in the non-abelian case which suggest the bold conjecture that a group with cofinite Zariski topology is necessarily either abelian or finite. We show that Tkachenko-Yaschenko theorem fails in the non-abelian case and we offer a natural counterpart in the general case using a partial Zariski topology and an appropriate stronger version of the property almost torsion-free.

Markov's problem for free groups

“…Suppose now that x ∈ X ∩ Y and E ∈ E . By (3), Recall that for every subset Z of a set X, the subgroup of F (X) generated by Z coincides with F (Z). In what follows, we shall always identify F (Z) with this subgroup of F (X).…”

“…Additional results on Z G , M G and P G for a non-commutative group G can be found in [12,13,3]. The paper is organized as follows.…”