Separating expansion from contraction and generalizing TOV condition in
  spherically symmetric models with pressure
  We investigate spherically symmetric solutions with pressure and discuss the
existence of a dividing shell separating expanding and collapsing regions. We
perform a 3+1 splitting and obtain gauge invariant conditions relating not only
the intrinsic spatial curvature of the shells to the ADM mass, but also a
function of the pressure which we introduce that generalises the
Tolman-Oppenheimer-Volkoff equilibrium condition. We consider the particular
case of a Lema\^itre-Tolman dust models with a cosmological constant (a
$\Lambda$-CDM model) as an example of our results.
