Some inherently ambiguous context-free languages

Prefixes of Infinite Words and Ambiguous Context-Free Languages

Inherently Ambiguous: Facial Expressions of Emotions, in Context

With a few yet increasing number of exceptions, the cognitive sciences enthusiastically endorsed the idea that there are basic facial expressions of emotions that are created by specific configurations of facial muscles. We review evidence that suggests an inherent role for context in emotion perception. Context does not merely change emotion perception at the edges; it leads to radical categor...

Some Results on Top-Context-Free Tree Languages

Top context free tree languages called cor gulier by Arnold and Dauchet constitute a natural subclass of context free tree languages In this paper we give further evidence for the importance of this class by exhibiting certain closure properties We systematically treat closure under the operations replacement and substitution as well as under the corresponding iteration operations Several other...

Nonterminal Complexity of Some Operations on Context-Free Languages

We investigate context-free languages with respect to the measure Var of descriptional complexity, which gives the minimal number of nonterminals which is necessary to generate the language. Especially, we consider the behaviour of this measure with respect to operations. For given numbers c1, c2, . . . , cn and an nary operation τ on languages we discuss the range of Var(τ(L1, L2, . . . , Ln))...

The Inclusion Problem for Some Subclasses of Context-Free Languages

− By a reduction to Post’s Correspondence Problem we provide a direct proof of the known fact that the inclusion problem for unambiguous context-free grammars is undecidable. The argument or some straightforward modification also applies to some other subclasses of context-free languages such as linear languages, sequential languages, and DSClanguages (i.e., languages generated by context-free ...