Uffe Flarup Pascal Koiran Laurent Lyaudet On the Expressive Power of Planar Perfect Matching and Permanents of Bounded Treewidth Matrices. 124-136 2007 conf/isaac/2007 ISAAC http://dx.doi.org/10.1007/978-3-540-77120-3_13 db/conf/isaac/isaac2007.html#FlarupKL07