Several results from classical computability theory (computability over discrete structures such as the natural numbers and strings over finite alphabets, due to Turing, Church, Kleene and others) have been shown to hold for a generalisation of computability theory over total abstract algebras, using for instance the model of \While\ computation. We present a number of results relating to computation on topological partial algebras, again using \While\ computation. We consider several results from the classical theory in the context of topological algebra of the reals: closure of semicomputable sets under finite union (Chapter \ref{chap:results1} Theorem \ref{thm:union_While_scomp_not_While_scomp}, p.\pageref{thm:union_While_scomp_not_While_scomp}), the equivalence of semicomputable and projectively (semi)computable sets (Chapter \ref{chap:results2} Theorem \ref{thm:proj_while_equivalents}, p.\pageref{thm:proj_while_equivalents}), and Post's Theorem (i.e.~a set is computable iff both it and its complement are semicomputable) (Appendix \ref{appendix:posts_theorem} Theorem \ref{thm:posts_general}, p.\pageref{thm:posts_general}). This research has significance in the field of scientific computation, which is underpinned by computability on the real numbers. We will consider a ``continuity principle", which states that computability should imply continuity; however, equality, order, and other total boolean-valued functions on the reals are clearly discontinuous. As we want these functions to be basic for the algebras under consideration, we resolve this incompatibility by redefining such functions to be partial, leading us to consider topological partial algebras. / Thesis / Master of Computer Science (MCS) / We investigate to what extent certain well-known results of classical computability theory on the natural numbers hold in the context of generalised computability theories on the real numbers.

It is known that orderings can be formed with settling time domination and strong settling time domination as relations on c.e. sets. However, it has been shown that no such ordering can be formed when considering computation time domination as a relation on $n$-c.e. sets where $n \geq 3$. This will be extended to the case of $2$-c.e. sets, showing that no ordering can be derived from computation time domination on $n$-c.e. sets when $n\geq 2$. Additionally, we will observe properties of the orderings given by settling time domination and strong settling time domination on c.e. sets, respectively denoted as $\mathcal{E}_{st}$ and $\mathcal{E}_{sst}$. More specifically, it is already known that any countable partial ordering can be embedded into $\mathcal{E}_{st}$ and any linear ordering with no infinite ascending chains can be embedded into $\mathcal{E}_{sst}$. Continuing along this line, we will show that any finite partial ordering can be embedded into $\mathcal{E}_{sst}$.

It is known that orderings can be formed with settling time domination and strong settling time domination as relations on c.e. sets. However, it has been shown that no such ordering can be formed when considering computation time domination as a relation on $n$-c.e. sets where $n \geq 3$. This will be extended to the case of $2$-c.e. sets, showing that no ordering can be derived from computation time domination on $n$-c.e. sets when $n\geq 2$. Additionally, we will observe properties of the orderings given by settling time domination and strong settling time domination on c.e. sets, respectively denoted as $\mathcal{E}_{st}$ and $\mathcal{E}_{sst}$. More specifically, it is already known that any countable partial ordering can be embedded into $\mathcal{E}_{st}$ and any linear ordering with no infinite ascending chains can be embedded into $\mathcal{E}_{sst}$. Continuing along this line, we will show that any finite partial ordering can be embedded into $\mathcal{E}_{sst}$.

Orientador: Walter Alexandre Carnielli / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Filosofia e Ciencias Humanas / Made available in DSpace on 2018-08-14T17:27:49Z (GMT). No. of bitstreams: 1 Agudelo_JuanCarlosAgudelo_D.pdf: 1223911 bytes, checksum: 92e4a3e06e1921aefd3476374d0726f2 (MD5) Previous issue date: 2009 / Resumo: Neste trabalho levantamos, e investigamos do ponto de vista conceitual, evidências de que a complexidade algorítmica pode ser vista como relativa à lógica. Propomos, para tanto, novos modelos de computação fundados sobre lógicas não-clássicas, estudando suas características quanto à expressabilidade computacional e eficiência. A partir desta visão, sugerimos um novo caminho para estudar a eficiência dos modelos de computação quântica, enfatizando a análise de uma lógica subjacente a tais modelos. O conteúdo da tese está estruturado da seguinte maneira: no primeiro capítulo apresentamos uma análise conceitual da noção de 'computação', indicando como este conceito tem mudado desde os trabalhos fundacionais da década de 1930, e discutindo se o conceito deve ser considerado como puramente físico, puramente lógicomatemático ou uma combinação de ambos. O Capítulo 2 introduz duas versões de 'máquinas de Turing paraconsistentes', usando sistemas lógicos diferentes e obtendo modelos com diferentes poderes computacionais (quanto à eficiência); tal resultado constitui uma primeira evidência a favor da relatividade lógica da computação que queremos defender. Outra evidência na mesma direção é apresentada no Capitulo 3, através da generalização dos circuitos booleanos para lógicas não-clássicas, em particular para a lógica paraconsistente mbC e para a lógica modal S5, e da análise do poder computacional de tais generalizações. O Capítulo 4 consiste numa introdução à computação quântica, para logo (no Capítulo 5) estabelecer algumas relações entre modelos de computação quântica e modelos de computação paraconsistente, de maneira a propor uma interpretação lógica dos modelos quânticos. No capítulo final (Capítulo 6) descrevemos várias relações entre mecânica quântica e lógica paraix consistente, relações estas que sugerem potencialidades com alto grau de relevância a respeito da abordagem paraconsistente dos fenômenos computacionais quânticos e que incitam a continuar explorando esta alternativa. / Abstract: This work provides evidences to view computational complexity as logic-relative, by introducing new models of computation through non-classical logics and by studying their features with respect to computational expressivity and efficiency. From this point of view, we suggest a new way to study the efficiency of quantum computational models consisting in the analysis of an underlying logic. The contents of the thesis is structured in the following way: the first chapter presents a conceptual analysis of the notion of 'computation', showing how this concept evolved since the decade of 1930 and discussing whether it can be considered a pure physical or a pure logic-mathematical concept, or a combination of both paradigms. Chapter 2 introduces two versions of 'paraconsistent Turing machines', by considering different logic systems and obtaining models with different computational capabilities (with respect to efficiency); such a result constitute a first evidence in favor of the logical relativity of computation that we are defending here. Another evidence in the same direction is presented in Chapter 3 through a generalization of boolean circuits to non-classical logics, particularly for the paraconsistent logic mbC and for the modal logic S5, and by analyzing the computational power of such generalizations. Chapter 4 consists in an introduction to quantum computation. This is used in Chapter 5 to establish some relationships between quantum and paraconsistent models of computation, in order to propose a logic interpretation of quantum models. The final chapter (Chapter 6) describes several connections between quantum mechanics and paraconsistent logic; such relationship suggests highly relevant potentialities in favor of the paraconsistent approach to quantum computation phenomena encouraging to continue exploring this alternative. / Doutorado / Logica / Doutor em Filosofia

Whereas early researchers in computability theory described effective computability in terms of such models as Turing machines, Markov algorithms, and register machines, a recent trend has been to use simple programming languages as computability models. A parallel development to this programming approach to computability theory is the current interest in systematic and scientific development and proof of programs. This paper investigates the feasibility of using formal proofs of programs in computability theory. After describing a framework for formal verification of programs written in a simple theoretical programming language, we discuss the proofs of several typical programs used in computability theory.

As soon as Bennett and Gill first demonstrated that, relative to a randomly chosen oracle, P is not equal to NP with probability 1, the random oracle hypothesis began piquing the interest of mathematicians and computer scientists. This was quickly disproven in several ways, most famously in 1992 with the result that IP equals PSPACE, in spite of the classes being shown unequal with probability 1. Here, we propose what could be considered strengthening of the random oracle hypothesis, using a stricter notion of what it means for a set to be 'large'. In particular, we suggest using largeness with respect to the Ramsey forcing notion. In this new context, we demonstrate that the set of oracles separating NP and coNP is 'not small', and obtain similar results for the separation of PSPACE from PH along with the separation of NP from BQP. In a related set of results, we demonstrate that these classes are all of the same descriptive complexity. Finally we demonstrate that this strengthening of the hypothesis turns it into a sufficient condition for unrelativized relationships, at least in the three cases considered here.