Carmel Domshlak Ronen I. Brafman Strucutre and Complexitiy in Planning with Unary Operators. 2000 conf/puk/2000 PuK http://www-is.informatik.uni-oldenburg.de/~sauer/puk2000/papers/domshlak.pdf db/conf/puk/puk2000.html#DomshlakB00