  We present a phenomenological approach (EPOS), based on the parton model, but
going much beyond, and try to understand proton-proton and deuteron-gold
collisions, in particular the transverse momentum results from all the four
RHIC experiments. It turns out that elastic and inelastic parton ladder
splitting is the key issue. Elastic splitting is in fact related to screening
and saturation, but much more important is the inelastic contribution, being
crucial to understand the data. We investigate in detail the rapidity
dependence of nuclear effects, which is actually relatively weak in the model,
in perfect agreement with the data, if the latter ones are interpreted
correctly.
