Published online by Cambridge University Press: 05 June 2014
Abstract. The “Turing Model”, in the form of “Classical Computability Theory”, was generalized in various ways. This paper deals with generalizations where computations may be infinite. We discuss the original motivations for generalizing computability theory and three directions such generalizations took. One direction is the computability theory of ordinals and of admissible structures. We discuss why Post's problem was considered the test case for generalizations of this kind and briefly how the problem was approached. This direction started with metarecursion theory, and so did the computability theory of normal functionals. We survey the key results of the computability theory of normal functionals of higher types, and how, and why, this theory led to the discovery and development of set recursion. The third direction we survey is the computability theory of partial functionals of higher types, and we discuss how the contributions by Platek on the one hand and Kleene on the other led to typed algorithms of interest in Theoretical Computer Science. Finally, we will discuss possible ways to axiomatize parts of higher computability theory.
Throughout, we will discuss to what extent concepts like “finite” and “computably enumerable” may be generalized in more than one way for some higher models of computability.
§1. Introduction. In this paper we will survey what we may call higher analogues of the Turing model. The Turing model, in the most restricted interpretation of the term, consists of the Turing machines as a basis for defining computable functions, decidable languages, semi-decidable languages and so forth.
To save this book to your Kindle, first ensure [email protected] is added to your Approved Personal Document E-mail List under your Personal Document Settings on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part of your Kindle email address below. Find out more about saving to your Kindle.
Note you can select to save to either the @free.kindle.com or @kindle.com variations. ‘@free.kindle.com’ emails are free but can only be saved to your device when it is connected to wi-fi. ‘@kindle.com’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.
Find out more about the Kindle Personal Document Service.
To save content items to your account, please confirm that you agree to abide by our usage policies. If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account. Find out more about saving content to Dropbox.
To save content items to your account, please confirm that you agree to abide by our usage policies. If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account. Find out more about saving content to Google Drive.