Showing papers in "Theoretical Computer Science in 1991"

TL;DR: The authors consider specifications consisting of a state machine that specifies safety requirements and an arbitrary supplementary property that specifies liveness requirements and show that under reasonable assumptions about the specifications, if S/ Sub 1/ implements S/sub 2/, then by adding auxiliary variables to S/ sub 1/ one can guarantee the existence of a refinement mapping.

TL;DR: It is shown that the computational problem of devising a strategy that achieves a given worst-case ratio to the optimum path in a graph is a universal two-person game, and thus PSPACE-complete, whereas optimizing the expected ratio is #P-hard.

TL;DR: The paper presents results on the generative capacity of mcfg's and also on the properties of mcfl's such as formal language-theoretic closure properties and it is shown that the time complexity of the membership problem for multiple context-free languages is O(ne).

TL;DR: Nondeterministic multivalued functions with values that are polynomially verifiable and guaranteed to exist form an interesting complexity class between P and NP, which is called TFNP and contains a host of important problems, whose membership in P is currently not known.

TL;DR: This work provides matching upper and lower bounds on the data-complexity of testing containment, membership and uniqueness for sets of possible worlds and shows that the certain fact problem is coNP-complete, even for a fixed first order query applied to a Codd-table.

TL;DR: This work derives corresponding formalisms for nets with structured tokens, based on term substitution, for conventional Petri nets based on place- and transition-invariants and algebraic specifications.

TL;DR: This paper describes an effective procedure for stratifying a real semi-algebraic set into cells of constant description size that compares favorably with the doubly exponential size of Collins' decomposition.

TL;DR: It is shown how an important proof method, which is a variant of Park's (1969) principle of fixpoint induction, can be used to prove the consistency of the static and the dynamic relational semantics of a small functional programming language with recursive functions.

TL;DR: A data structure is presented such that each entry in the adjacency matrix of a planar graph can be looked up in constant time, and can be constructed in linear time.

TL;DR: The complexity of decision problems that can be solved by a polynomial-time Turing machine that makes a bounded number of queries to an NP oracle is studied and the Boolean hierarchy and the bounded query hierarchies either stand or collapse together are studied.

TL;DR: In this article, the authors present indexed categories which model uniformly defined families of categories, and suggest that they are a useful tool for the working computer scientist, and several examples are given.

TL;DR: This paper presents a general framework in which decision procedures can be developed based on a combination of generating function techniques for counting, and complex analysis techniques for asymptotic estimations, and exposes here the theory of exact analysis in terms of generating functions for four different domains.

TL;DR: It is proved that for m ⩾1, card( A m ) = 1+∑ m i =1 ( m − i +1) ϕ ( i ) where A m is the set of factors of length m of all the Sturmian words and ϕ is the Euler function.

TL;DR: Eilenberg's Equality Theorem is extended to a general result which implies that the multiplicity equivalence problem of two (nondeterministic) multitape finite automata is decidable and solves a long standing open problem in automata theory.

TL;DR: The contribution of the paper is to exhibit an interesting class of programs having a default semantics, called effectively stratifiable programs, and to provide a constructive definition of well-founded models of logic programs.

TL;DR: It is shown how operations such as natural join and projection —which are fundamental to relational database design—can be generalized, and this generalized framework is used to give characterizations of several relational database concepts including functional dependencies and universal relations.

TL;DR: It is proved that no sound and complete simple loop check exists, even for programs without function symbols, and an implementation of the closed world assumption of Reiter and a query evaluation algorithm for these classes of logic programs are obtained.

TL;DR: A nondeterministic calculus of closures for the evaluation of λ-calculus, which is based, not on symbolic evaluation (β-reduction), but on the paradigm of environments and closures, as in the old SECD machine, or in the more recent Categorical Abstract Machine (CAM).

TL;DR: This paper shows how to adapt the semantics of a first order typed language, with semantics of S, in a simple set theoretic way, obtaining a semantics that satisfies, in addition to some obvious requirements, also the property that: $S'~s$ is included in S, whenever $s < t$.

TL;DR: This paper solves an open problem raised by Stern (1985) — “Is finite-automaton aperiodicity PSPACE-complete?” by providing an affirmative answer and characterize the exact complexity of two other problems considered by Stern: (1) dot-depth-one language recognition and (2) piecewise testable language recognition.

TL;DR: The basic aim is to investigate the possibility to give direct inductive definitions of semantical notions exploring the structure of the given notion rather than to think of such notions as indirectly presented by a formal system or given by a definition, together with a proof of its correctness in terms of recursion on some well-founded structure.

TL;DR: It is shown that the unfold/fold rules can be extended to rules for stratified programs and it is proved that both the success set and the finite failure set of a stratified program are preserved.

TL;DR: The main goal of this paper is to present a unified theory for the semantics of Horn and disjunctive logic programs by extending the fixpoint semantics and the operational or procedural semantics to the class of disjunctions logic programs and proving their equivalence using techniques similar to the ones used for Horn programs.

TL;DR: Advantages of the approach are: proofs about data refinement are simplified; more general techniques ofData refinement are suggested; and a style of program development is encouraged in which data refinements are calculated directly without proof obligation.

TL;DR: It is shown that the degree of ambiguity of a finitely ambiguous nondeterministic finite automaton (NFA) with n states is at most 5n2·nn, and there is a simple criterion which characterizes the infinite degree of ambiguous of an NFA, and which is decidable in polynomial time.

TL;DR: In this paper, the authors studied the complexity of polynomial reconstruction on a finite field K of small characteristic and showed that the time complexity depends critically on the degree m of the extension field of K from which the arguments are to be chosen.

TL;DR: This paper surveys and compares different techniques investigated in order to integrate negation in rule-based query languages and presents the declarative semantics of logic programs with negation based on fixpoint techniques, based on three valued logic and based on non-monotonic logics.

TL;DR: It is shown that such problems of permutation groups of the infinite complete binary tree yield natural complete sets that separate time and space complexity classes if they are distinct.