Degrees of Transducibility

摘要

Our objects of study are infinite sequences and how they can be transformed into each other. As transformational devices, we focus here on Turing Machines, sequential finite state transducers and Mealy Machines. For each of these choices, the resulting transducibility relation ≥ is a preorder on the set of infinite sequences. This preorder induces equivalence classes, called degrees, and a partial order on the degrees. For Turing Machines, this structure of degrees is well-studied and known as degrees of unsolvability. However, in this hierarchy, all the computable streams are identified in the bottom degree. It is therefore interesting to study transducibility with respect to weaker computational models, giving rise to more fine-grained structures of degrees. In contrast with the degrees of unsolvability, very little is known about the structure of degrees obtained from finite state transducers or Mealy Machines.