Alex Nash Sven Koenig Maxim Likhachev Incremental Phi*: Incremental Any-Angle Path Planning on Grids. 1824-1830 2009 IJCAI http://ijcai.org/papers09/Papers/IJCAI09-303.pdf conf/ijcai/2009 db/conf/ijcai/ijcai2009.html#NashKL09