We present algebraic conditions on constraint languages Î“ that ensure the hardness of the constraint satisfaction problemCSP(Î“ ) for complexity classes L, NL, P, NP andModpL. These criteria also giveâ€¦ (More)

The study of finite automata and regular languages is a privileged meeting point of algebra and logic. Since the work of BÃ¼chi, regular languages have been classified according to their descriptiveâ€¦ (More)

We consider the problem of testing whether a given system of equations over a fixed finite semigroup S has a solution. For the case where S is a monoid, we prove that the problem is computable inâ€¦ (More)

The temporal logic operators atnext and atprevious are alternatives for the operators until and since. P atnext Q has the meaning: at the next position in the future where Q holds it holds P . Weâ€¦ (More)

Unlike the wreath product, the block product is not associative at the level of varieties. All decomposition theorems involving block products, such as the bilateral version of Krohnâ€“Rhodesâ€™ theorem,â€¦ (More)

We study the computational complexity of solving equations and of determining the satis ability of programs over a xed nite monoid. We partially answer an open problem of [4] by exhibitingâ€¦ (More)