Unmixed bipartite graphs and sublattices of the Boolean lattices
  The correspondence between unmixed bipartite graphs and sublattices of the oolean lattice is discussed. By using this correspondence, we show the existence of squarefree quadratic initial ideals of toric ideals arising from minimal vertex covers of unmixed bipartite graphs. 
Juergen Herzog, Takayuki Hibi, Hidefumi Ohsugi