We would like to thank the anonymous referees of Artificial Intelligence Review whose comments were crucial in revising the content of this paper. We are also indebted to Patrick Suppes (CSLI), Wlodek Zadrozny (IBM T. J. Watson), Rohit Parikh (CUNY), and Ramesh Patil (USC-ISI) for their moral support. Finally, Melanie Willow (Kluwer) deserves our gratitude for her kind assistance beyond the call of duty.
Akman's research is supported in part by a grant (TBAG--992) from the Scientific and Technical Research Council of Turkey (TÜBITAK).