Undecidability in omega-regular languages



: Halava V, Harju T, Karhumaki J

Publisher: IOS PRESS

: 2006

: Fundamenta Informaticae

: FUNDAMENTA INFORMATICAE

: FUND INFORM

: 73

: 1-2

: 119

: 125

: 7

: 0169-2968


In the infinite Post Correspondence Problem an instance (h, g) consists of two morphisms h and 9, and the problem is to determine whether or not there exists an infinite word a such that h(alpha) = g(alpha). In the general case this problem was shown to be undecidable by K. Ruohonen (1985). Recently, it was proved that the infinite PCP is undecidable already when the domain alphabet of the morphisms consists of at least 9 letters. Here we show that the problem is undecidable for instances where the morphisms have a domain of 6 letters, when we restrict to solutions of omega-languages of the form R-omega where R is a given regular language.



Last updated on 2025-14-10 at 09:56