T. Eiter, W. Faber, M. Fink, S. Woltran:
"Complexity results for answer set programming with bounded predicate arities and implications";
Annals of Mathematics and Artificial Intelligence (invited), 51 (2007), 2-4; 123 - 165.
http://dx.doi.org/10.1007/s10472-008-9086-5