1. Aho A.V., Hopcroft J.E., Ullman J.D.: Data Structures and Algorithms, Addison-Wesley, Reading, MA, 1983.
2. Carlsson M.: Freeze, Indexing, and Other Implementation Issues in the WAM, in Lassez J.L.(ed.), Logic Programming — Proceedings of the 4th International Conference — Volume 1, MIT Press, Cambridge, MA, 1987.
3. Carlsson M., Widen J.: Sicstus Prolog Users Manual, Swedish Institute of Computer Science, SICS/R-88/88007C, 1990.
4. Holzbaur C.: Specification of Constraint Based Inference Mechanisms through Extended Unification, Dept. of Medical Cybernetics & Artificial Intelligence, University of Vienna, Dissertation, 1990.
5. Huitouze S.le: A new data structure for implementing extensions to Prolog, in Deransart P. and Maluszunski J.(eds.), Programming Language Implementation and Logic Programming, Springer, Heidelberg, 136–150, 1990.