Density of the Commensurability Groups of Uniform Tree Lattices Original Research Article

Let X be a universal cover of a finite connected graph, and Γ a group acting discretely and cocompactly on X, i.e., a uniform lattice on X. We announce a proof of the conjecture of H. Bass and R. Kulkami (J. Amer. Math. Soc. No. 4 (1990), 843-902) that the commensurability group of Γ is dense in the automorphism group of X.