Languages and Scanners

In this paper, we are interested in a special class of automata, called scanners. These machines can be considered as a model for computations that require only “local” information. Informally, a scanner is an automaton equipped with a finite memory and a “sliding” window of a fixed length. In a typical computation, the sliding window is moved from left to right on the input, so that the scanner can remember the factors of length smaller than or equal to the size of the window. In view of these factors, the scanner decides whether or not the input is accepted or rejected.