I am pleased to present this issue, most of which is devoted to a single subject-Spatial Reasoning. Our guest editor is Avi Kak, of Purdue University. Avi called me in the Summer of 1987, very enthused about a workshop he had recently attended. The idea of a "theme issue" on spatial reasoning sounded like a winner to me. I asked Avi to take the responsibility for selecting and editing the articles, and he agreed.

R1, a knowledge-based configurer of VAX-11 computer systems, began to be used over a year ago by Digital Equipment Corporation's manufacturing organization. The success of this program and the existence at DEC of a newly formed group capable of supporting knowledge-based programs has led other groups at DEC to support the development of programs that can be used in conjunction with RI. This paper describes XSEL, a program being developed at Carnegie-Mellon University that will assist salespeople in tailoring computer systems to fit the needs of customers. XSEL will have two kinds of expertise: it will know how to select hardware and software components that fulfil the requirements of particular sets of applications, and it will know how to provide satisfying explanations in the computer system sales domain.

A programming language based on sets; motivation and examples.

The equivalence problem for program schemes, or for programs, is reduced to the proving of a theorem in second-order logic. This work extends Manna's first-order logic reductions. Some examples of the technique are given together with a suggested method for obtaining proofs in special cases by firstorder methods. INTRODUCTION Several workers in recent years have considered using techniques and ideas of various mathematical theories of computation for proving interesting results about computer programs. This paper is concerned with two of these approaches.

Knowledge-Based Backtracking," is a principal researcher for the Advanced Technology Center, Boeing Computer Services, P.O. Jackson Y. Read, coauthor of "Real-Time Knowledge-Based Systems," is a senior analyst and associate investigator of the independent research project on real-time knowledge-based Jack Breese, who reviewed The Principles and Applications of Decision Analysis, systems at Lockheed Artificial Intelligence is with Rockwell, 444 High Street, Palo Alto, California 94301. Preston A. Cox, coauthor of "Real-Time Knowledge-Based Systems," is a scientific programmer specialist for Lockheed's Space System Division in Sunnyvale, Patrick Saint-Dizier is chairman of California. James L. Schmidt, coauthor of "Real- " is a research computer scientist Bryan M. Kramer, author of the Time Knowledge-Based Systems," is a in the Department of Computer review of Expert Systems, is affiliated scientific programmer and associate Science, Carnegie-Mellon University, with Xerox Canada, Inc., 5650 Yonge investigator of the independent Pittsburgh, Pennsylvania 15213 Street, North York, Ontario M2M research project on real-time knowledge-based 4G7, Canada. Intelligence Center, 2710 Sand Practitioners Should Know about the Thomas J. Laffey, coauthor of "Real-Hill Road, Menlo Park, California Law," is an attorney practicing with Time Knowledge-Based Systems," is a 94025. Nutter, McClennen & Fish, One research scientist and the principal International Place, Boston, Massachusetts investigator of the independent Jeffrey Stout is on the research staff of 02210-2699. She coedited the research Victor Lesser, coauthor of "Approximate in progress, "New Mexico State University's Processing in Real-Time Problem Yorick Wilks is the director of the Computing Research Laboratory."

Sargur N. Srihari is a professor and acting chairman of the Department of Computer Science, State University of New York (SUNY) at Buffalo. The author of "Recognizing Address Blocks on Mail Pieces," Srihari is an associate editor of the journal Pattern Recognition and is chairman of the technical committee on text-processing applications of the International Mike Baird, who coauthored the tribute to Kvetoslav Prazdny, is manager of Association for Pattern Recognition. Srihari is also currently directing two Intelligence Center 1185 Coleman Avenue, Santa Clara, California 95052. Jeffrey Stone is a consultant who watches the computer industry and Jonathan J. Hull is a research assistant Digital Equipment Corporation that reports new developments and trends. The opinions expressed "Recognizing Address Blocks on Mail address is Knowledge Systems Corporation, in his article are his own. Jeffrey Stout is on the research staff of computer vision, and artificial intelligence. An Expert Elevator report on AI and education, is an Buffalo, where he is also currently Designer that Uses Knowledge-Based associate professor in the Department working on his Ph.D. His research Backtracking." of Mathematics and Computer Science interests include image processing, at Millersville University, computer graphics, and computer segmentation Jay M. Tenenbaum, who coauthored Millersville, Pennsylvania 1755 1. Palumbo is a the tribute to Kvetoslav Prazdny, is a coauthor of "Recognizing Address Schlumberger Fellow at the Schlumberger John McDermott is a principal scientist Blocks on Mail Pieces."

In this article we discuss a method for learning useful conditions on the application of operators during heuristic search. Since learning is not attempted until a complete solution path has been found for a problem, credit for correct moves and blame for incorrect moves is easily assigned. We review four learning systems that have incorporated similar techniques to learn in the domains of algebra, symbolic integration, and puzzle-solving. We conclude that the basic approach of learning from solution paths can be applied to any situation in which problems can be solved by sequential search. Finally, we examine some potential difficulties that may arise in more complex domains, and suggest some possible extensions for dealing with them.

This paper describes XSEL, a program being developed at Carnegie-Mellon University that will assist salespeople in tailoring computer systems to fit the needs of customers. XSEL will have two kinds of expertise: it will know how to select hardware and software components that fulfil the requirements of particular sets of applications, and it will know how to provide satisfying explanations in the computer system sales domainIn Hayes, J. E., Michie, D., and Pao, Y.-H. (Eds.), Machine Intelligence 10. Ellis Horwood.

Carnegie-Mellon University has established a Robotics Institute to bring its expertise in engineering, science, and industrial administration to bear upon the problem of national industrial productivity. The institute has been established to undertake advanced research and development in seeing, thinking robots and intelligent systems, and to facilitate transfer of this technology to industry. The Institute is engaged in broad programs of research in robotics, artificial intelligence, manufacturing technology, micro-electronics technology, and computer science. The Institute offers the promise of dramatic advances that will not only improve the productivity of all types of employees but also lead to improvements in the "quality of life" for all.

Planning is the process of formulating an intended course of action. In this paper we present a model of planning and describe the current version of an INTERLISP simulation of the model. We also review psychological results which confirm the model's basic assumptions for human planning behavior.