The ω-inequality problem for concatenation hierarchies of star-free languages
Jorge Almeida, Ondřej Klíma, Michal Kunc · Forum Mathematicum · 2017
Abstract The problem considered in this paper is whether an inequality of ω-terms is valid in a given level of a concatenation hierarchy of star-free languages. The main result shows that this problem is decidable for all (integer and half) levels of the Straubing–Thérien hierarchy.