Context-free Control Research Articles

Towards characterizing bisimilarity of value-passing processes with context-free control

A value-passing version of normed context-free processes is considered, where process behaviours depend on a global state of data variables. The problem of characterizing bisimilarity of such processes is posed. A solution of the formulated problem is presented for a restricted class of processes and possibilities of extending the result are discussed. The presented solution exploits a tableau decision method for pure, normed, context-free processes: based on a tableau, a system of implications is formulated, solution of which characterizes bisimulation equivalence for a pair of value-passing processes.

A note on the intersection of context-free languages

It is shown that a) there is an equal matrix language which cannot be written as a finite intersection of context-free languages and b) any finite intersection of context-free languages can be generated by a regular conditional grammar with context-free control languages.

A recursive and a grammatical characterization of the exponential-time languages

We characterize the class of all languages which are acceptable in exponential time by means of recursive and grammatical methods. (i) The class of all languages which are acceptable in exponential time is uniquely characterized by the class of all (0-1)-functions which can be generated, starting with the initial functions of the Grzegorczyk-class E 2, by means of subtitution and limited recursion of the form f( x, y + 1) = h( x, y), f( x, y), f( x, l( x, y))), l( x, y) ⩽ y. (ii) The class of all languages which are acceptable in exponential time is equal to the class of all languages generated by context-sensitive grammars with context-free control sets.

The structure generating function of some families of languages

The structure generating function of a language enumerates the number of distinct words contained in the language with respect to their length. Given any language generated unambiguously by a grammar with context-free control language or generated n -unambiguously by a state grammar with context-free control language or generated unambiguously by a tuple grammar with contextfree control language, a method is described which yields a system of equations, whose unique solution is the structure generating function.

A comparison of the Ponzo illusion with a textural analogue

The inappropriate constancy scaling notion of geometric illusions was explored by employing a textural analogue of the Ponzo figure. Ten Ss estimated the length of a horizontal line by equating it with varying companion lines in the context of the Ponzo figure, a textural analogue, and a baseline control in which the lines appeared with no surrounding contours. The textural analogue had the added feature of imposing no contours at the ends of the horizontal lines. It was found that length estimates were significantly different between the horizontals of the Ponzo figure and control stimuli, but not between the texture figure and a context-free control. The results suggest that inappropriate constancy scaling plays a minor role at best in the perception of geometric illusions.