In this paper we consider a simple Markov chain for bipartite graphs with
given degree sequence on n vertices. We show that the mixing time of this
Markov chain is bounded above by a polynomial in n in case of {\em
semi-regular} degree sequence. The novelty of our approach lays in the
construction of the canonical paths in Sinclair's method.Comment: 47 pages, submitted for publication. In this version we explain
explicitly our main contribution and corrected a serious flaw in the cycle
decompositio