We give a fresh introduction to the Khovanov Homology theory for knots and links,
with special emphasis on its extension to tangles, cobordisms and 2–knots. By
staying within a world of topological pictures a little longer than in other articles on
the subject, the required extension becomes essentially tautological. And then a
simple application of an appropriate functor (a “TQFT”) to our pictures takes them
to the familiar realm of complexes of (graded) vector spaces and ordinary
homological invariants.
Keywords
2–knots, canopoly,
categorification, cobordism, Euler characteristic, Jones
polynomial, Kauffman bracket, Khovanov, knot invariants,
movie moves, planar algebra, skein modules, tangles, trace
groups