  A model of nonlinear resonance as a periodically perturbed pendulum is
considered, and a new method of analytical estimating the width of a chaotic
layer near the separatrices of the resonance is derived for the case of slow
perturbation (the case of adiabatic chaos). The method turns out to be
successful not only in the case of adiabatic chaos, but in the case of
intermediate perturbation frequencies as well.
