“…In this form, the kinetic energy as well as constraint J(r 0 , r 1 ) = l > 1 are invariant with respect to natural action of group SO(1, 2) on R 3 . Hence, as in the case of the spherical dumbbell, we define a frame {b 1 , b 2 , b 3 } in which the dumbbell rests. As we assumed that l > 1, vectors r 0 and r 1 are not parallel, so z = C(r 0 , r 1 ) = 0.…”