  The deformation parameters beta and gamma together with the two-quasiparticle
excitations are taken into account, for the first time, as coordinates within a
symmetry conserving (angular momentum and particle number) generator coordinate
method. The simultaneous consideration of collective as well as single particle
degrees of freedom allows us to describe soft and rigid nuclei as well as the
transition region in between.
  We apply the new theory to the study of the spectra and transition
probabilities of the 156-172Er isotopes with a Pairing plus Quadrupole residual
interaction. Good agreement with the experimental results is obtained for most
of the observables studied and with the same quality for the very soft and the
strongly deformed nuclei.
