On Recognizable Languages of Infinite Pictures

Abstract: In a paper, Altenbernd, Thomas and W\"ohrle have considered acceptance of languages of infinite two-dimensional words (infinite pictures) by finite tiling systems, with the usual acceptance conditions, such as the B\"uchi and Muller ones, firstly used for infinite words. The authors asked for comparing the tiling system acceptance with an acceptance of pictures row by row using an automaton model over ordinal words of length $\omega^2$. We give in this paper a solution to this problem, showing that all languages of infinite pictures which are accepted row by row by B\"uchi or Choueka automata reading words of length $\omega^2$ are B\"uchi recognized by a finite tiling system, but the converse is not true. We give also the answer to two other questions which were raised by Altenbernd, Thomas and W\"ohrle, showing that it is undecidable whether a B\"uchi recognizable language of infinite pictures is E-recognizable (respectively, A-recognizable).