Chilukuri K. Mohan, Mandayam K. Srivas. Negation with Logical Variables in Conditional Rewriting. In Nachum Dershowitz, editor, Rewriting Techniques and Applications, 3rd International Conference, RTA-89, Chapel Hill, North Carolina, USA, April 3-5, 1989, Proceedings. Volume 355 of Lecture Notes in Computer Science, pages 292-310, Springer, 1989.