Definition 1. Let G be a group. G is said to be residually finite if the intersection of all normal subgroups of G of finite index in G is trivial. For a survey of results on residual finiteness and related properties, see Mag-nus, Karrass, and Solitar [6, Section 6.5]. We shall present a proof of the following well known theorem, which is important for Kharlampovich [4, 5]. See also O. V. Bele...

We construct minimal laminations by hyperbolic surfaces whose generic leaf is a disk and contain any prescribed family of with precise control the topologies that appear. The are constructed via towers finite coverings for which we need to develop relative version residual finiteness may be independent interest. main step in establishing this obtain covers on second systole surface, done Append...

We discuss residual finiteness and several related separability conditions for the class of monoid acts, namely weak subact separability, strong complete separability. For each these four conditions, we investigate which monoids have property that all their (finitely generated) acts satisfy condition. In particular, prove that: over a finite are completely separable (and hence other three condi...