ARTIFICIAL INTELLIGENCE VOLUME 98, NUMBERS 1-2, JANUARY 1998 Abstracted/indexed in: ACM Computing Reviews, Applied Science and Technology Abstracts, Applied Science and Technology Index, CAD/CAM Abstracts, Cambridge Scientific Abstracts, Computer Abstracts, Current Contents: Engineering, Technology & Applied Science, Current Contents: Social & Behavioral Sciences, Engineering Index/Compendex, Information Science Abstracts, INSPEC Information Services, Mathematical Reviews, Science Citation Index, Social Sciences Citation Index, Sociological Abstracts, Zentralblatt fr Mathematik CONTENTS N.L. Tinkham Schema induction for logic program synthesis A.L. Lansky Localized planning with action-based constraints J. Liu A method of spatial reasoning based on qualitative trigonometry 137 G. Kern-lsberner Characterizing the principle of minimum cross-entropy within a condi- tional-logical framework 169 M. Freund Preferential reasoning in the perspective of Poole default logic 209 R.H. Wilson Geometric reasoning about assembly tools 237 C. Boutilier A unified model of qualitative belief change: a dynamical systems perspective 281 R.1. Brafman, J.Y. Halpern and Y. Shoham On the knowledge requirements of tasks 317 E. Tsang No more “Partial” and “Full Looking Ahead” (Research Note) 351 D. Bojadziev and M. Gams Addendum to “Sloman’s view of Gédel’s sentence” (Research Note) 363 Forthcoming Papers 367 Author Index 369 ContentsDirect, the free e-mail alerting service, delivers the table of contents for this journal directly to your PC, prior to publication. The quickest way to register for ContentsDirect is via the Internet at: http://www.elsevier.nl/locate/ContentsDirect. [f you don’t have access to the Internet you can register for this service by sending an e-mail message to [email protected] - specifying the title of the publication you wish to register for. || | Keep track of recently published papers via the journal's home page on the WWW: http://www.elsevier.ni/locate/artint 0004-3702( 199801 )98:1;1-V