  Falbel, Koseleff and Rouillier computed a large number of boundary unipotent
CR representations of fundamental groups of non compact three-manifolds. Those
representations are not always discrete. By experimentally computing their
limit set, one can determine that those with fractal limit sets are discrete.
Many of those discrete representations can be related to (3,3,n) complex
hyperbolic triangle groups. By exact computations, we verify the existence of
those triangle representations, which have boundary unipotent holonomy. We also
show that many representations are redundant: for n fixed, all the (3,3,n)
representations encountered are conjugate and only one among them is
uniformizable.
