The downward closure of a word language is the set of all (not necessarily contiguous) subwords of its members. It is well-known that the downward closure of any language is regular. While theâ€¦ (More)

The separability problem for word languages of a class C by languages of a class S asks, for two given languages I and E from C, whether there exists a language S from S that includes I and excludesâ€¦ (More)

We investigate the monoid of transformations that are induced by sequences of writing to and reading from a queue storage. We describe this monoid by means of a confluent and terminating semi-Thueâ€¦ (More)

We consider the computational power of silent transitions in one-way automata with storage. Specifically, we ask which storage mechanisms admit a transformation of a given automaton into one thatâ€¦ (More)

In their paper [24], Myasnikov, Nikolaev, and Ushakov started the investigation of classical discrete integer optimization problems in general non-commutative groups. Among other problems, theyâ€¦ (More)

It is shown that the knapsack problem, which was introduced by Myasnikov et al. for arbitrary finitely generated groups, can be solved in NP for graph groups. This result even holds if the groupâ€¦ (More)

Two kinds of multiset automata with a storage attached, varying only in their ability of testing the storage for emptiness, are introduced, as well as normal forms. Their accepting power and relationâ€¦ (More)

It is shown that the knapsack problem, which was introduced by Myasnikov et al. for arbitrary finitely generated groups, can be solved in NP for every graph group. This result even holds if the groupâ€¦ (More)