The MPEG compression standard1 will be used for the distribution of many new digital TV services. Also, MPEG compression is already being used for contributions into the studio, because of bandwidth/bit-rate restrictions on some incoming connections. In addition, there will be pressure to use high levels of compression in future TV archives in order to give on-line access to thousands of hours ...

In the theory of formal languages, the understanding of concatenation hierarchies of regular languages is one of the most fundamental and challenging topic. In this paper, we survey progress made in the comprehension of this problem since 1971, and we establish new generic statements regarding this problem.

We investigate two operators on classes of regular languages: polynomial closure ( $$Pol$$ ) and Boolean $$Bool$$ ). apply these to group languages $$\mathcal {G}$$ their well-suited extensions {G} ^+$$ , which is the least algebra containing $$ $$\{\varepsilon \}$$ . This yields $$Bool(Pol(\mathcal {G}))$$ ^+))$$ These form first level in important classifications languages, called concatenati...

We consider the state complexity of basic operations on tree languages recognized by deterministic unranked tree automata. For the operations of union and intersection the upper and lower bounds of both weakly and strongly deterministic tree automata are obtained. For tree concatenation we establish a tight upper bound that is of a different order than the known state complexity of concatenatio...