Forbidden Patterns for Ordered Automata
Ondřej Klíma, Libor Polák · Journal of automata, languages and combinatorics · 2020
The contribution concerns decision procedures in the algebraic theory of regular languages. Among others, various versions of forbidden patterns or configurations in automata are treated in the existing literature. Basically, one looks for certain subgraphs of the minimal automaton of a given language to decide whether this language does not belong to a given significant class of regular languages. We survey numerous known examples and we build a general theory covering the most of familiar ones. The chosen formalism differs from existing ones and the generalization to ordered automata enables us to reformulate some of known examples in a uniform shape. We also describe certain sufficient assumptions on the forbidden pattern which ensure that the corresponding class of languages forms a robust class in the sense of natural closure properties.