  We discuss here a generalization of a theorem by Dunfield stating that the
peripheral holonomy map, from the character variety of a 3-manifold to the
A-polynomial is birational. Dunfield's proof involves the rigidity of maximal
volume. The volume is still an important ingredient in this paper.
Unfortunately at this point no complete proof is done. Instead, a conjecture is
stated about the volume function on the character variety that would imply the
generalized birationality result.
