  We review theory of the leading twist nuclear shadowing, and describe
phenomenon of post-selection suppression of leading parton spectrum (effective
fractional energy losses) in the proximity of the black disk regime. We argue
that $2 \to 2$ mechanism dominates in the inclusive leading pion production in
d-Au collisions and explain that the post-selection naturally explains both the
magnitude of the suppression of the forward pion production in d-Au collisions
and the pattern of the forward - central correlations. At the same time this
pattern of correlations rules out $2\to 1$ mechanism as the main source of the
inclusive leading pion yield. It is demonstrated that the mechanism of the
double parton interactions gives an important contribution to the production of
two leading pions in $pp$ scattering opening a new way to study correlations of
leading quarks in the nucleon. The same mechanism is enhanced in $dAu \to
\pi^0\pi^0 +X$ collisions and explains the dominance of $\Delta\phi$
independent component and suppression of the away side peak.
