  We study the non-linear gravitational collapse of dark matter into halos
through numerical N-body simulations of Lemaitre-Tolman-Bondi void models. We
extend the halo mass function formalism to these models in a consistent way.
This extension not only compares well with the simulated data at all times and
radii, but it also gives interesting clues about the impact of the background
shear on the growth of perturbations. Our results give hints about the
possibility of constraining the background shear via cluster number counts,
which could then give rise to strong constraints on general inhomogeneous
models, of any scale.
