Philip N. Klein Shay Mozes Oren Weimann Shortest paths in directed planar graphs with negative lengths: a linear-space <i>O</i>(<i>n</i> log<sup>2</sup> <i>n</i>)-time algorithm. 236-245 2009 SODA http://doi.acm.org/10.1145/1496770.1496797 conf/soda/2009 db/conf/soda/soda2009.html#KleinMW09