“…Thus it seems like a natural line of inquiry to try to distinguish the fundamental groups of 3-manifolds by looking at their finite quotients, since finite quotients of fundamental groups correspond to finite-sheeted regular coverings, so that commensurability of 3-manifolds coincides with commensurability of their fundamental groups. Tying together all of the information about finite quotients of fundamental groups through an inverse limit leads us to the concept of the profinite completion of the group (see Definition 2.1), and to profinite rigidity (see Definition 2.6); this thus follows in the path laid down by [12], [14], and [18], among many others. In particular, Wilton and Zaleskii in [17,Thm 8.4] show that the profinite completion of a geometric 3-manifold group determines its geometry, and further, in [18], they show that the profinite completion of a 3-manifold group also determines the JSJ decomposition of the manifold.…”