Title: Geometrically finite amalgamations of hyperbolic 3-manifold groups are not LERF,
Abstract: We prove that, for any two finite volume hyperbolic $3$-manifolds, the
amalgamation of their fundamental groups along any nontrivial geometrically
finite subgroup is not LERF. This generalizes the author's previous work on
nonLERFness of amalgamations of hyperbolic $3$-manifold groups along abelian
subgroups. A consequence of this result is that closed arithmetic hyperbolic
$4$-manifolds have nonLERF fundamental groups. Along with the author's previous
work, we get that, for any arithmetic hyperbolic manifold with dimension at
least $4$, with possible exceptions in $7$-dimensional manifolds defined by the
octonion, its fundamental group is not LERF.