REGULARITY OF LANGUAGES DEFINED BY FORMAL SERIES WITH ISOLATED CUT POINT
Let L-phi,L-lambda = {omega is an element of Sigma* vertical bar phi(omega) > lambda} be the language recognized by a formal series phi : Sigma* -> R with isolated cut point lambda. We provide new conditions that guarantee the regularity of the language L-phi,L-lambda in the case that phi is rational or phi is a Hadamard quotient of rational series. Moreover the decidability property of such conditions is investigated.
hadamard quotient formal power series regular languages