Language Theoretic Properties

Abstract

Closure properties and decidability properties are among the basic classes of questions investigated in formal language theory for every class of generative mechanisms. We call them “language theoretic”, but such questions are also of a practical interest. For instance, remember from Chapter 2 the use of operations with languages (and of corresponding closure properties) when trying to prove that a given language (English, for example) does not belong to a given family. Similarly, decidability problems are involved in the very definition of a contextual grammar and of the generated language: checking whether or not a substring of a string we want to derive (in the internal mode) belongs to a given selector amounts at solving the membership problem with respect to this selector.