Further Remarks on the Operational Nonterminal Complexity
Abstract
For a regular language L, let Var(L) be the minimal number of nonterminals necessary to generate L by right linear grammars. Moreover, for natural numbers k1,k2,…,kn and an n-ary regularity preserving operation f, let the range gVarf(k1,k2,…,kn) be the set of all numbers k such that there are regular languages L1,L2,…,Ln with Var(Li)=ki for 1≤i≤n and Var(f(L1,L2,…,Ln))=k. We show that, for the circular shift operation Circ, gVarCirc(n) is infinite for all n, and we completely determine the set gVarCirc(2). Moreover, we give a precise range for the left right quotient and a partial result for the left quotient. Furthermore, we add some values to the range for the operation intersection which improves the result of [2].
Communicated by Martin Kutrib