  We evaluate the charge and spin susceptibilities of the 2D attractive Hubbard
model and we compare our results with Montecarlo simulations on the same model.
We discuss the possibility to include topological Kosterlitz-Thouless
superconducting fluctuations in a standard perturbative approach substituting
in the fluctuation propagator the Ginzburg-Landau correlation length with the
Kosterlitz-Thouless correlation length.
