hyperarithmetical hierarchy

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• Hyperarithmetical theory — In recursion theory, hyperarithmetic theory is a generalization of Turing computability. It has close connections with definability in second order arithmetic and with weak systems of set theory such as Kripke–Platek set theory. It is an… …   Wikipedia

• Arithmetical hierarchy — In mathematical logic, the arithmetical hierarchy, arithmetic hierarchy or Kleene hierarchy classifies certain sets based on the complexity of formulas that define them. Any set that receives a classification is called arithmetical. The… …   Wikipedia

• Borel hierarchy — In mathematical logic, the Borel hierarchy is a stratification of the Borel algebra generated by the open subsets of a Polish space; elements of this algebra are called Borel sets. Each Borel set is assigned a unique countable ordinal number… …   Wikipedia

• Analytical hierarchy — In mathematical logic and descriptive set theory, the analytical hierarchy is a higher type analogue of the arithmetical hierarchy. It thus continues the classification of sets by the formulas that define them. The analytical hierarchy of… …   Wikipedia

• Арифметическое множество — В теории множеств и математической логике, множество натуральных чисел называется арифметическим, если оно может быть определено формулой в языке арифметики первого порядка, то есть если существует такая формула с одной свободной переменной что… …   Википедия

• Computability theory — For the concept of computability, see Computability. Computability theory, also called recursion theory, is a branch of mathematical logic that originated in the 1930s with the study of computable functions and Turing degrees. The field has grown …   Wikipedia

• Recursion theory — Recursion theory, also called computability theory, is a branch of mathematical logic that originated in the 1930s with the study of computable functions and Turing degrees. The field has grown to include the study of generalized computability… …   Wikipedia

• Reduction (recursion theory) — In computability theory, many reducibility relations (also called reductions, reducibilities, and notions of reducibility) are studied. They are motivated by the question: given sets A and B of natural numbers, is it possible to effectively… …   Wikipedia

• Reverse mathematics — is a program in mathematical logic that seeks to determine which axioms are required to prove theorems of mathematics. The method can briefly be described as going backwards from the theorems to the axioms. This contrasts with the ordinary… …   Wikipedia

• Descriptive set theory — In mathematical logic, descriptive set theory is the study of certain classes of well behaved subsets of the real line and other Polish spaces. As well as being one of the primary areas of research in set theory, it has applications to other… …   Wikipedia

• Set theory — This article is about the branch of mathematics. For musical set theory, see Set theory (music). A Venn diagram illustrating the intersection of two sets. Set theory is the branch of mathematics that studies sets, which are collections of objects …   Wikipedia