  Mikhail Khovanov in math.QA/9908171 defined, for a diagram of an oriented
classical link, a collection of groups numerated by pairs of integers. These
groups were constructed as homology groups of certain chain complexes. The
Euler characteristics of these complexes are coefficients of the Jones
polynomial of the link. The goal of this note is to rewrite this construction
in terms more friendly to topologists. A version of Khovanov homology for
framed links is introduced. For framed links whose Kauffman brackets are
involved in a skein relation, these homology groups are related by an exact
sequence.
