  We solved numerically the implicit, trascendental equation that defines the
eigenenergy surface of a degenerating isolated doublet of unbound states in the
simple but illustrative case of the scattering of a beam of particles by a
double barrier potential. Unfolding the degeneracy point with the help of a
contact equivalent approximant, crossings and anticrossings of energies and
widths, as well as the changes of identity of the poles of the S-matrix are
explained in terms of sections of the eigenenergy surfaces.
