In computer science, more specifically in automata and formal language theory, nested words are a concept proposed by Alur and Madhusudan as a joint generalization of words, as traditionally used for modelling linearly ordered structures, and of ordered unranked trees, as traditionally used for modelling hierarchical structures. Finite-state acceptors for nested words, so-called nested word automata, then give a more expressive generalization of finite automata on words.
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Regular tree grammar
In Computer Science, a regular tree grammar (RTG) is a formal grammar that describes a set of directed trees.
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Pushdown automaton
In automata theory, a pushdown automaton (PDA) is a variation of finite automaton that can make use of a stack containing data.
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Monadic predicate calculus
In logic, the monadic predicate calculus is the fragment of predicate calculus in which all predicate letters are monadic (that is, they take only one argument), and there are no function letters. All atomic formulae have the form, where is a predicate letter and is a variable. Monadic predicate logic can be contrasted with polyadic predicate logic, which uses predicates (called many-place predicates) that take two or more arguments.
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Kleene star
In mathematical logic and computer science, the Kleene star (or Kleene operator or Kleene closure) is a unary operation, either on sets of strings or on sets of symbols or characters. The application of the Kleene star to a set V is written as V*. It is widely used for regular expressions, which is the context in which it was introduced by Stephen Kleene to characterise certain automata, where it means "zero or more".
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Omega language
An ¿-language is a set of infinite-length sequences of symbols.
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Context-free language
In formal language theory, a context-free language is a language generated by some context-free grammar. The set of all context-free languages is identical to the set of languages accepted by pushdown automata.
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