  Calculations of the one-hole spectral function of 16O for small missing
energies are reviewed.
  The self-consistent Green's function approach is employed together with the
Faddeev equations technique in order to study the coupling of both
particle-particle and particle-hole phonons to the single-particle motion. The
results indicate that the characteristics of hole fragmentation are related to
the low-lying states of 16O and an improvement of the description of this
spectrum, beyond the random phase approximation, is required to understand the
experimental strength distribution.
  A first calculation in this direction that accounts for two-phonon states is
discussed.
