Sequential grammars and automata with valences

نویسندگان

Henning Fernau

Ralf Stiebe

چکیده

We discuss the model of valence grammars, a simple extension of context-free grammars. We show closure properties of context-free valence languages over arbitrary monoids. Chomsky and Greibach normal form theorems and an iteration lemma for context-free valence grammars over the groups Z are proved. The generative power of di4erent control monoids is investigated. In particular, we show that context-free valence grammars over 6nite monoids or commutative monoids have the same power as valence grammars over 6nite groups or commutative groups, respectively. c © 2002 Elsevier Science B.V. All rights reserved.

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