  Perturbation theory is shown to be working in the IR limit of pure SU(3)
Yang-Mills theory in Landau gauge by an unconventional setting of the
perturbative expansion. A dynamical mass is predicted for the gluon and the
lattice data are reproduced fairly well by a second-order expansion, without
any free parameter. The effective running coupling is small in the IR and the
approximation can be improved by inclusion of higher order terms.
