It is proved that conjunctive grammars can still be parsed in cubic time and that the notion of the derivation tree is retained, which gives reasonable hope for their practical applicability.Expand

It is proved that the set of scattered substrings of a language recognized by an n-state DFA requires a DFA with at least 2$^{n/2-2}$ states (the known upper bound is 2$^n$), with witness languages… Expand

The state complexity of the star of union of an m-state DFA language and an n-state DFA language is proved to be 2 m+n−1−2 m−1−2 n−1+1 for every alphabet of at least two letters. The state complexity… Expand

If the Dyck language is augmented with neutral symbols, the characterization holds for every context-free language using a letter-to-letter homomorphism, as long as the language contains no one-symbol strings.Expand

Their equivalence implies the equivalence of several other formal systems, including a certain restricted class of Turing machines and a certain type of language equations, thus giving further evidence for the importance of the language family they all generate.Expand

A new generalization of context-free grammars is introduced: Boolean grammars allow the use of all set-theoretic operations as an integral part of the formalism of rules. Rigorous semantics for these… Expand

This work looks at stateless multihead finite automata in their two-way and one-way, deterministic and nondeterministic variations, and shows that the emptiness problem for stateless 2-head two- way automata is undecidable.Expand

Nondeterministic finite automata (NFA) with at most one accepting computation on every input string are known as unambiguous finite automata (UFA). This paper considers UFAs over a one-letter… Expand

The closure properties of the language family generated by linear conjunctive grammars are investigated; the main result is its closure under complement, which implies that it is closed under all set-theoretic operations.Expand

For 2- and 3-letter alphabets, it is proved 2 ⊖(n2) state complexity, and a tight 2n 2 + 1 lower bound is established for the nondeterministic state complexity of this operation using a binary alphabet.Expand