Polynomial and abstract subrecursive classes

摘要

The reducibility “polynomial time computable in” for arbitrary functions isintroduced. It generalizes Cook's definition from sets to arbitrary functions. A complexity-theoretic as well as a syntactic characterization is given and their equivalence is shown. This equivalence and the naturalness of both definitions give evidence that our notion is “correct.” The computable functions are classified into polynomial classes according to this reducibility. The ordering of these classes under set inclusion is studied. Honest classes are introduced and using them, the classification is related to the computational complexity of the functions classified. The algebraic structure of honest classes is also investigated.In Section II abstract subrecursive reducibilities are introduced. An axiomaticdefinition in purely recursion-theoretic terms is given; in particular, no reference to a particular machine model is needed. The definition is in the spirit of Strong's and Wagner's characterizations of basic recursive function theories. All known reducibilities are abstract reducibilities. The algebraic structure of abstract classes is explored.