@inproceedings{DBLP:conf/lpnmr/GebserLL07, title = {Head-Elementary-Set-Free Logic Programs}, author = {Gebser, Martin and Lee, Joohyung and Lierler, Yuliya}, booktitle = {{LPNMR}}, pages = {149--161}, publisher = {Springer}, series = {Lecture Notes in Computer Science}, volume = {4483}, year = {2007} }