  In the context of count-in-cells statistics, the joint probability
distribution of the density in two concentric spherical shells is predicted
from first first principle for sigmas of the order of one. The agreement with
simulation is found to be excellent. This statistics allows us to deduce the
conditional one dimensional probability distribution function of the slope
within under dense (resp. overdense) regions, or of the density for positive or
negative slopes. The former conditional distribution is likely to be more
robust in constraining the cosmological parameters as the underlying dynamics
is less evolved in such regions. A fiducial dark energy experiment is
implemented on such counts derived from Lambda-CDM simulations.
