  This paper contains a categorification of the sl(k) link invariant using
parabolic singular blocks of category O. Our approach is intended to be as
elementary as possible, providing combinatorial proofs of the main results of
Sussan. We first construct an exact functor valued invariant of webs or
'special' trivalent graphs labelled with 1, 2, k-1, k satisfying the MOY
relations. Afterwards we extend it to the sl(k)-invariant of links by passing
to the derived categories. The approach using foams appears naturally in this
context. More generally, we expect that our approach provides a representation
theoretic interpretation of the sl(k)-homology, based on foams and the
Kapustin-Lie formula. Conjecturally this implies that the Khovanov-Rozansky
link homology is obtained from our invariant by restriction.
