Effective embedding of residually hyperbolic groups into direct products   of extensions of centralizers
  For any torsion-free hyperbolic group $\Gamma$ and any group $G$ that is fully residually $\Gamma$, we construct algorithmically a finite collection of homomorphisms from $G$ to groups obtained from $\Gamma$ by extensions of centralizers, at least one of which is injective. When $G$ is residually $\Gamma$, this gives a effective embedding of $G$ into a direct product of such groups. We also give an algorithmic construction of a diagram encoding the set of homomorphisms from a given finitely presented group to $\Gamma$. 
Olga Kharlampovich, Jeremy Macdonald
math.GR