3010463
Equality Languages and Fixed Point Languages
This paper considers equality languages and fixed-point languages of homomorphisms and deterministic gsm mappings. It provides some basic properties of these classes of languages. We introduce a new subclass of dgsm mappings, the so-called symmetric dgsm mappings. We prove that (unlike for arbitrary dgsm mappings) their fixed-point languages are regular but not effectively obtainable. This result has various consequences. In particular we strengthen a result from Ehrenfeucht, A., and Rozenberg, G. [(1978), Theor. Comp. Sci. 7, 169–184] by pointing out a class of homomorphisms which includes elementary homomorphisms but still has regular equality languages. Also we show that the result from Herman, G. T., and Walker, A. [(1976), Theor. Comp. Sci. 2, 115–130] that fixed-point languages of DIL mappings are regular, is not effective.
30357320
The Power to Two-Way Deterministic Checking Stack Automata
Abstract It is well known that nondeterministic two-way checking stack automata recognize NSPACE( n ). We show that deterministic two-way checking stack automata have the same power as deterministic two-way two-head finite automata. The easy proof is based on the closure under inverse deterministic two-way GSM mappings of the deterministic two-way two-head finite automaton languages.
13469765
Decidability of the Finiteness of Ranges of Tree Transductions
Abstract The finiteness of ranges of tree transductions is shown to be decidable for TBY + , the composition closure of macro tree transductions. Furthermore, TBY + definable sets and TBY + computable relations are considered, which are obtained by viewing a tree as an expression that denotes an element of a given algebra. A sufficient condition on the considered algebra is formulated under which the finiteness problem is decidable for TBY + definable sets and for the ranges of TBY + computable relations. The obtained result applies in particular to the class of string languages that can be defined by TBY + transductions via the yield mapping. This is a large class which is proved to form a substitution-closed full AFL.
11003400
Passes and Paths of Attributive Grammars
An attribute grammar is pure (left-to-right) multi-pass if a bounded number of left-to-right passes over the derivation tree suffice to compute all its attributes. There is no requirement, as for the usual multi-pass attribute grammars, that all occurrences of the same attribute are computed in the same pass. It is shown that the problem of determining whether an arbitrary attribute grammar is pure multipass, is of inherently exponential time complexity. For fixed k > 0, it can be decided in polynomial time whether an attribute grammar is pure k-pass. The proofs are based on a characterization of pure multi-pass attribute grammars in terms of paths through their dependency graphs. A general result on dependency paths of attribute grammars relates them to (finite-copying) top-down tree transducers. The formal power of k-pass attribute grammars increases with increasing k. Formally, multi-pass attribute grammars are less powerful than arbitrary attribute grammars.
1862248
Monotonicity and Persistence in Preferential Logics
An important characteristic of many logics for Artificial Intelligence is their nonmonotonicity. This means that adding a formula to the premises can invalidate some of the consequences. There may, however, exist formulae that can always be safely added to the premises without destroying any of the consequences: we say they respect monotonicity. Also, there may be formulae that, when they are a consequence, can not be invalidated when adding any formula to the premises: we call them conservative. We study these two classes of formulae for preferential logics, and show that they are closely linked to the formulae whose truth-value is preserved along the (preferential) ordering. We will consider some preferential logics for illustration, and prove syntactic characterization results for them. The results in this paper may improve the efficiency of theorem provers for preferential logics.
35737768
A Compositional Reasoning System for Executing Nonmonotonic Theories of Reasoning
In this paper a system was developed using the compositional modelling environment DESIRE (framework for DEsign and Specification of Interacting REasoning components). This environment for the development of compositional reasoning systems and multi-agent systems has been succesfully used to design various types of reasoning systems and multi-agent systems and applications in particular domains. The DESIRE sofware environment offers a graphical editor, an implementation generator and an execution environment to execute specifications automatically.
34994233
Iterated deterministic substitution
SummaryDeterministic substitution of languages means substituting the same word (from a given language) for all occurrences of a symbol. For an arbitrary family K of languages the notion of deterministic K-iteration grammar is introduced, which is essentially the iteration of a finite number of deterministic substitutions of languages from K. The families of languages generated by these grammars are investigated.
7110538
Only Persistence Makes Nonmonotonicity Monotonous
An important characteristic of many logics for artificial intelligence is that they are nonmonotonic. This means that adding a formula to the premises can destroy some of the consequences. There may exist formulae that can always be safely added to the premises without destroying any of the consequences: they respect monotonicity. We consider three preferential logics for which we analyze the class of formulae which respect monotonicity. For each of the three logics we show that this class is equal to the class of formulae preserved under going to more preferred models, and we provide syntactic characterizations of these classes.
20050455
Clique-Width for 4-Vertex Forbidden Subgraphs
Clique-width of graphs is a major new concept with respect to efficiency of graph algorithms. The notion of clique-width extends the one of treewidth, since bounded treewidth implies bounded clique-width. We give a complete classification of all graph classes defined by forbidden induced subgraphs of at most four vertices with respect to bounded or unbounded clique-width.