Recursively Enumerable Languages Research Articles

Grammars, derivation modes and properties of indexed and type-0 languages

In this paper a notion of a grammar is defined which is an extension of a context-free grammar by index productions of the form Aƒ → B and A → Bƒ. With these productions one can ‘compute’ information coded by strings of indices. We consider two modes of derivation which distribute this information over context-free productions in a different way. The two derivation modes yield the classes of indexed and type-0 languages respectively. The context-free-like structure of the grammar is used as a tool to investigate normal-form transformations, Dyck languages and homomorphic characterizations.

Mixed product and asynchronous automata

We show the interest of the mixed (or synchronous) product for studying traces and trace languages in the free partially commutative monoids. We use this product to construct particular asynchronous automata and we show that each asynchronous automaton is the image by a strictly alphabetic morphism of a mixed product of automata. Then we use this result and Zielonka's theorem (1984) to obtain a result similar to Mezei's theorem in the free partially commutative monoids by showing that each recognizable trace language is the homomorphic image of some finite union of synchronous products of recognizable languages.

The family of one-counter languages is closed under quotient

We study, first, the operation of quotient in connection with rational transductions. We show, afterwards, that Rocl, the family of one counter languages is closed under quotient by a context-free language. On the contrary, every recursively enumerable language is the quotient of two linear languages.

Hiérarchies de concaténation

Is it well-known that there exists a one-to-one correspondence between varieties of recognizable languages and varieties of finite semigroups. New hierarchies of varieties of languages (based on the concatenation product) are defined and an algebraic description of the corresponding hierarchies of varieties of semigroups is given. Various well-known hierarchies are obtained as particular cases. The construction is based on the following result: if a language L is recognized by the Schutzenberger product of the monoids M_0, ..., M_n, then L belongs to the Boolean closure of the set of languages of the form L_{i_0}a_1L_{i_1} ... a_rL_{i_r} (0 ≤ i_0 < i_1 < ... < i_r ≤ n) where the ak are letters and the Lik are recognized by M_{i_k} (0 ≤ k ≤ r). Decidability and inclusion problems are also discussed.

Pattern matching in trees and nets

Rational patterns are used to specify recognizable tree languages. It is shown that, given a rational patternp and a treet, one can decide inO(¦p¦·¦t¦) steps whether there is some match ofp int. Problems of this kind generalized to forests or nets are shown to be NP-complete.

Le spectacle de l'exécution dans la France d'Ancien Régime

« Rappelons-nous », suggère Lucien Febvre, dans un de ses articles consacrés aux alliances et appuis de l'histoire auprès de la psychologie, « tel récit de ce temps, le coupable agenouillé, les yeux bandés, la tête sur le billot… Déjà l'homme rouge brandit sa redoutable épée nue. Et brusquement des cris, un cavalier à fond de course qui envahit la place en brandissant un parchemin, Grâce,grâce… ». Temps fort de l'expression des émotions, le spectacle de l'exécution met en jeu, dans chaque individu, des sentiments instinctifs aussi puissants qu'ils peuvent être changeants : haine, colère, mépris, peur, compassion, admiration. Exprimés et renforcés par des comportements collectifs, ces sentiments individuels reposent sur un climat affectif ou un climat de sensibilité parfois propre à un petit groupe, mais aussi capable de déferler sur le grand nombre comme une épidémie mentale. Champ du combat des idées et des volontés politiques, ce climat d'une époque ou d'une génération, qui s'exprime dans le discours dominant ou dans les changements institutionnels, implique à la fois une certaine nouveauté, mais aussi la prise en compte des comportements acquis de longue date.

Generalization of the Ginsburg-Rice Schützenberger fixed-point theorem for context-sensitive and recursive-enumerable languages

The paper generalizes the Ginsburg-Rice Schützenberger ALGOL-like fixed-point theorem showing that every λ-free context-sensitive (recursive-enumerable) language is a component of the least fixed-point of a system of equations in the form X = F( X), where X = ( X 1,…, X t ), F = ( F 1,…, F t ), t⩾1 and for all i, 1⩽ i⩽ t, F i are regular expre ssions over the alphabet of operations: {union, concatenation, Kleene+ (∗) closure, nonerasing finite substitution (arbitrary finite substitution), intersection}. Fixed-point characterization theorems for these families of languages are also presented.

Uniform Interpretations of Grammar Forms

Encouraged by positive experiences with so-called uniform-interpretations of L-forms, we investigate in this paper a suitable analogous definition of uniform interpretations of grammar forms. Concerning CF grammar forms it is shown that a rich variety of language families can be obtained. CF grammar forms with a single variable are extensively examined both with regard to generative capacity (including a characterization of subregular, sublinear and subfinite index families) and with regard to the notion of goodness and badness. Concerning non-CF grammar forms it is shown that each of the families of EOL-, ETOL-, matrix-, scattered context-, context sensitive, type 0-languages (and many others) can be obtained by using interpretations of one form specific to this family.

Effects of vestibular stimulation on spontaneous use of verbal language in developmentally delayed children.

The relationship between vestibular stimulation and language development in a group of five primary trainable mentally deficient and five developmentally retarded preschoolers was studied. Subjects received vestibular stimulation prior to a free play situation and were monitored for spontaneous recognizable language use. Results indicated an increase in spontaneous verbal language use for both groups immediately after the stimulation periods, and suggest vestibular stimulation as an effective nonverbal intervention method for the facilitation of spontaneous language.

Fixed Point Languages, Equality Languages, and Representation of Recursively Enumerable Languages

Fixed point languages and equality languages of homomorphisms and dgsm mappings are consid- ered. Some basic properties of these classes of languages are proved, and it is shown how to use them to represent recursively enumerable sets. In particular, very simple languages are introduced which play the same role for the class of recursively enumerable languages that the Dyck languages play for the class of context-free languages. Finally, a new type of acceptor for defining equality languages is introduced. KEY WOADS AND PHRASES: equality language, fLxed point language, recursively enumerable language, determin- istic sequential machine, Turing machine, Post correspondence problem, shuffle, AFL generator, representation of languages

Language performance on visual processing tasks in right hemisphere lesion cases

Seven language tests were constructed or adapted to assess the performance of three groups of 10 right-handed adult subjects: a right hemisphere lesion (RHL) group, a left hemisphere lesion (LHL) group, and a neurologically normal (NN) control group. Both the LHL and RHL groups produced poorer scores than the NN group on six of the seven tests. On two of the six significant tests, the RHL performed more poorly than the NN group. Analyses of words uttered during an oral story telling test indicated that the RHL group told significantly fewer complete stories using significantly more nouns, adjectives, and conjunctions than the NN group. On a 7-point scale, three judges rated the overall communication abilities of the RHL group as having “mild problems,” a significantly different rating than the ratings of the LHL and NN groups. The findings suggest that underlying visual spatial and perceptual deficits may be accompanied by clearly recognizable language differences in certain subjects.

Recognizable languages and finite semilattices of groups

Recognizable languages and finite semilattices of groups

A generalized approach to formal languages

A generalization of ranked alphabets, many-sorted alphabets, is studied. The concepts of finite automaton, regular, recognizable, equational, and context free languages are generalized to sets over these new alphabets. It is shown that the derivation trees of a context free set are always characterized by some recognizable set over a related many-sorted alphabet. Previous theory is drawn as a special case of these results and new results are advanced. A number of suggestions about language theory are made.

Language recognition by marking automata

An off-line, memory-restricted Turing machine model, the marking automaton (MA) is presented here as a device strictly intermediate between finite and linear bounded automata. Although much more restricted than the latter, MA are shown capable of recognizing, deterministically, various kinds of context-free (CF) languages and an important related class, as well as such non-CF languages as {xx} . It is not known whether all CF languages are recognizable by MA; however, among the familiar subclasses shown to consist of MA recognizable languages are the Dyck, standard, and bounded CF languages. More importantly, each member of the class of structured CF languages, consisting of all structural descriptions (Phrase-markers) of the sentences in a CF language, is shown to be MA recognizable. The closure of the MA recognizable languages under various set (e.g., boolean) operations is revealed in the proof that all bounded CF languages are MA recognizable.