The separability of formal languages

The Separability of Formal Languages

— We introducé the concept of a separator, a concept voeaker than aparser or a recognizer; however a separator can be usedvery conveniently when speedis important andaprecise error recovery is not mandatory. We distinguish between internai and external séparation criteria and show hom a set of these criteria isforming a hierarchy of more and more complex separators. Résumé. — On introduit Ie co...

Formal Languages

Factorization in Formal Languages

We consider several novel aspects of unique factorization in formal languages. We reprove the familiar fact that the set uf(L) of words having unique factorization into elements of L is regular if L is regular, and from this deduce an quadratic upper and lower bound on the length of the shortest word not in uf(L). We observe that uf(L) need not be context-free if L is context-free. Next, we con...

Towards Nominal Formal Languages

We introduce formal languages over infinite alphabets where words may contain binders. We define the notions of nominal language, nominal monoid, and nominal regular expressions. Moreover, we extend history-dependent automata (HD-automata) by adding stack, and study the recognisability of nominal languages.

Automata and formal languages