A perspective on assumption-based truth maintenance
We have now had almost a decade of experience with ATMS-based problem solvers. Unfortunately it appears that some of the properties which led to its initial success are now the very properties which are causing problems as we try to scale up to larger tasks. Therefore one of the more active areas of current ATMS research is the investigation of additional mechanisms to control the combinatorial explosion without sacrificing its inherent advantages (usually known as focusing techniques).
de Kleer, J. A perspective on assumption-based truth maintenance. Artificial Intelligence. 1993 February; 59 (1-2): 63-67.