Path: utzoo!mnetor!uunet!husc6!think!ames!ucbcad!ucbvax!smu.CSNET!leff From: leff@smu.CSNET (Laurence Leff) Newsgroups: comp.doc.techreports Subject: tr-input/uklirb.x Message-ID: <8712091107.AA13123@ucbvax.Berkeley.EDU> Date: 7 Dec 87 14:26:24 GMT Sender: daemon@ucbvax.BERKELEY.EDU Organization: The ARPA Internet Lines: 823 Approved: techreports@smu.csnet This is our latest list of abstracts of SEKI REPORTS and SEKI WORKING PAPERS for both 1986 and 1987. PhD theses can be ordered at a nominal fee of US$ 10, SEKI REPORTS will cost US$ 2, and SEKI WORKING PAPERS (which are mostly written in German) will cost US$ 1.50, unless there is an exchange agreement. There is, however, another way to obtain SRs and SWPs. You can subscribe to all papers published during a year at a price of US$ 60. You will get each SR and SWP immediately after its publication. The fee covers both postage and packing. If you want to subscribe, please write (don't e-mail) and enclose a cheque. The subscription will end after one year unless you explicitly order and pay for another year. If you want to order any publications, please enclose a cheque payable to the university with the appropriate amount either in US$ or its equivalent in your own currency. Cash is welcome, too. Please, send your orders to the following address: Scarlet Noekel Universitaet Kaiserslautern Fachbereich Informatik Postfach 3049 6750 Kaiserslautern West Germany Phone: +49-631-205-2802 UUCP: ...!mcvax!unido!uklirb!scarlet ------------------------------------------------------------------------- SEKI REPORTS SR-86-01 bis SR-86-20 SEKI-REPORT SR-86-01 K.-H.Blaesius Consruction of Equality Graphs Abstract: The theoretical and practical problems of equality rea- soning in Automated Deduction are notorious. A new method is presented to cope with the enormous search space that usually ar- ises when equational axioms are present. Starting from an empty graph a production system constructs graphs which represent solu- tions for simpler problems defined by abstraction. These graphs contain global information and are plans for guiding the search for a proof of the original problem, represented in the final graph. The construction of equality graphs is based on the idea to search for the differences between two terms by seperating to- plevel symbol and subterms of a functional term. The impact of the explicit representation of information contained in the inference system on the control of inferences is discussed. Fi- nally the method is compared to other equality reasoning methods. SEKI-REPORT-SR-86-02 Ch. Beierle, A. Voss Specification, horizontal composition and parameterization of algebraic implementations Abstract: Loose specifications of abstract data types (ADTs) have many nonisomorphic algebras as models. An implementation between two loose specifications should therefore consider many abstrac- tion functions together with their source and target algebras. Just like specifications are stepwise refined to restrict their class of models, implementations should be stepwise refinable to restrict the class of abstraction functions. In this scenario specifications and implementations can be developed interwovenly. We suggest to have implementation specifications analo- gously to loose ADT specifications: Implementations have signa- tures, models, axioms and sentences thus constituting an institu- tion. Implementation specifications are the theories of this in- stitution and refinements between implementation specifications are its theory morphisms. In this framework, implementations between parameterized specifications and horizontal composition of implementations turn out to be special cases of the more powerful concept of parameterized implementations, which allow to instantiate an im- plementation by substituting a subimplementation by another im- plementation. SEKI-REPORT-SR-86-03 M. Reinfrank, M. Beetz, H. Freitag, J. Klug Kapri: A rule based non-monotonic inference engine with an in- tegrated reason maintenance system Abstract: KAPRI (Kaiserslautern Augmented Production Rule Inter- preter) uses rules of the form if I unless I then I . For such a rule to be fired, its monotonic if-antecedents are required to match the current database, while none of its non-monotonic unless-antecedents does. The current state of a KAPRI-system is represented by a dependency network composed of assertions and corresponding justifications for believing in them in terms of belief respectively disbelief in other assertions. This network is maintained by a reason maintenance system, KL-DNMS (Kaiserslautern Dependency Network Management System), that re- vises the current belief status with respect to every modifica- tion due to the firing of a rule or to the addition/retraction of a basic fact. In the present paper, we describe a very simple first version of KAPRI, and discuss some key issues that arise from augmenting production rules by an UNLESS-part, and from integrating a pro- duction rule-based inference engine with a reason-maintenance system. SEKI-REPORT-SR-86-04 H. Boley A Relational/Functional Integration with valued Clauses Abstract: The RELFUN programming language is introduced as an at- tempt to integrate the capabilities of the relational and func- tional styles. Definitions of functions and relations are speci- fied uniformly by valued Horn clauses, where rules return the value of their rightmost premise. Functional nestings are flat- tened to relational conjunctions, using a purified version of PROLOG's is-primitive. RELFUN functions may have non-ground argu- ments, like relations, and/or return non-ground values; their in- put and output arguments can be inverted like those of relations. Higher-order functions are definable as (function-)valued clauses, with funarg problems being avoided by the standard renaming of clause variables. RELFUN's operational semantics is specified as an abstract machine, which also yields its first (e-mailable) FRANZ LISP implementation. SEKI-REPORT-SR-86-05 H.-J. Buerckert Some Relationships between Unification, Restricted Unification and Matching Abstract: We present restricted T-unification that is unification of terms under a given equational theory T with the restriction that not all variables are allowed to be substituted. Some rela- tionships between restriced T-unification, unrestriced T- unification and T-matching (one-sided T-unification) are esta- blished. Our main result is that, in the case of an almost col- lapse free equational theory the most general restricted unifiers and for certain termpairs the most general matchers are also most general unrestricted unifiers; this does not hold for more gen- eral theories. Almost collapse free theories are theories, where only terms starting with projection symbols may collapse (i.e. to be T-equal) to variables. SEKI-REPORT-SR-86-06 R. Goebel Completion of Globally Finite Term Rewriting Systems for Induc- tive Proofs Abstract: The Knuth-Bendix Algorithm (KBA) is not able to com- plete term rewriting systems with cyclic rules such as the commu- tativity. This kind of rules cause cycles in a reduction chain. This problem may be solved by an extension of the KBA for global- ly finite term rewriting systems. For a globally finite term rewriting system, cycles may occur in a reduction chain, but for each term there is only a finite set of reductions. A confluent and globally finite term rewriting sytem R provides a decision procedure for equality induced by R: Two terms are equal iff there is a common term in their reduction sets. This extension requires new methods for testing the global fin- iteness and a new confluence test, because local confluence does not imply global confluence for globally finite relations. In this paper we give a theoretical framework for this extension. We will show how this theory can be applied to term rewriting sys- tems, if we are mainly interested in the initial algebra which is induced by the set of rules. SEKI-REPORT-SR-86-07 M. Schmidt-Schauss Unification Properties of Idempotent Semigroups Abstract: Unification in free idempotent semigroups is of unifi- cation type zero, i.e. there are unifiable terms s,t but there is no minimal, complete set of unifiers for these two terms. Unifi- cation in free idempotent semigroups is strongly complete, i.e. the unification problemis always solvable with unifier {x , t}, even if x occurs in t. We give a generalization of the usual unification hierarchy and demonstrate that the number of independent unifiers in A+I- unifier sets is not bounded. It is known that there is a conditional, canonical term rewriting system for idempotent semigroups. To strengthen this result, we show that there can be no unconditional and finite rewriting sys- tem. SEKI-REPORT-SR-86-08 M. Schmidt-Schauss Some Undecidable Classes of Clause Sets Abstract: The undecidability of finitely generated stable transi- tive relations on free terms is proved in an elementary way and then used to show the undecidability of the implication A^B of two clauses A and B. The implication is decidable in the case A has at most two literals that are complementary unifinable after renaming. Application of the undecidability of transitive rela- tions yields more classes of clause sets that have an undecidable satisfiability problem: clause sets consisting of two clauses with two literals each (2-clauses) and in addition 2 ground un- its, clause sets consisting of a single 3-clausse and arbitrarily many (non-ground) units and clause sets conssting of a 4-clause and arbitrarily many ground units. Finally we show the undecida- bility of the so-called D-clause sets, where a D-clause is a Horn-clause of the form Q1(x1) Y while-like specialization is studied in this language: the cut > initial cut restriction, which improves both readability and parallelization of PROLOG programs. For accessing LISP from PROLOG, we permit LISP predicates as goals, and LISP functions as right-hand sides of the is- predicate. In the other direction, the first n PROLOG solutions can be re- turned as a LISP list. LISPLOG.2 augments the trace and break tools already available in LISPLOG.1 by an (initial) +cut-indicator+/+manual cutter+ for making the cuts in the search tree observable and in- teractive. For improving efficiently, the originally recursive in- terpreter is reformulated iteratively, the binding environment is represented as an array structure, and the database is indexed by predicates and arguments. As the main application, LISPLOG runs a knowledge-based system, m-UNIXPERT, for diagnosing printing problems. SEKI-WORKING-PAPER SWP-86-09 (in German) Franz Kammermeier LISPLOG im Kontext anderer LISP/PROLOG-Vereinheitlichungen Abstract: Since 1979 a lot of functional/relational languages integrating LISP and PROLOG have been described in the litera- ture. In this paper it is tried to find the position of LISPLOG in the context of ten important other hybrids, which are mainly LISP based, e.g. LOGLISP, LM-Prolog and Symbolics Prolog. After a short introduction and a general view of these hybrids, firstly the integration of programming styles is compared, namely the correspondence of LISP/PROLOG data structures and the fa- cilities to access one formalism from the other. Implementation techniques of PROLOG interpreters, like implementation of con- trol, representation of term instances and database indexing, are examined in the second part, with the emphasis being on LISP as the implementation language.The comparison is supplemented by a short description of compilation techniques for PROLOG (in LISP) used by compilers of the treated languages. Finally, some conclusions for present and future improvements of LISPLOG are outlined. SEKI-WORKING-PAPER SWP-86-10 (in German) Ansgar Bernardi Ein Indexierungskonzept fr LISPLOG-Datenbasen Abstract: LISPLOG is a LISP/PROLOG integration explored at the Universitaet Kaiserslautern.To improve the performance of the LISPLOG interpreter, an indexing concept has been developed and implemented. Higher efficiency is gained by eliminating unnecessary unifications. Matching clauses are selected using the predicate and one con- stant atomic argument of the conclusion. A special combination of shared lists and binary trees is maintained by the indexing pro- cedure to make this selection rather fast.The user may optionally specify the indexing argument; the default-argument is changeable when installing the system. The indexing concept and the imple- mented algorithms and data structures are fully described in this paper, together with a complete source-listing (FRANZ LISP) of the implementation.