Let X and Y be smooth projective varieties over C. They are
called {\it D-equivalent} if their derived categories of bounded complexes of
coherent sheaves are equivalent as triangulated categories, while {\it
K-equivalent} if they are birationally equivalent and the pull-backs of their
canonical divisors to a common resolution coincide. We expect that the two
equivalences coincide at least for birationally equivalent varieties. We shall
provide a partial answer to the above problem in this paper.Comment: 25 pages, minor chang