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PERs in HAω I: Basic constructions and choice principles
Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Mathematics, Algebra, Geometry and Logic.
2011 (English)Report (Other academic)
Abstract [en]

We study the approximation of sets by partial equivalence rela-tions (PERs) in HAω - this construction is usually considered in type theory.In this rst part, we start with the basic denitions, and introduce notions ofequality, inclusion, and quotients of PERs. We then show that PERs form anitely complete and nitely cocomplete category, with all constructions given.We also make a detailed investigation of extensional choice principles.

Place, publisher, year, edition, pages
2011. , 35 p.
Series
U.U.D.M. report / Uppsala University, Department of Mathematics, ISSN 1101-3591 ; 2011:17
National Category
Algebra and Logic
Research subject
Mathematical Logic
Identifiers
URN: urn:nbn:se:uu:diva-159876OAI: oai:DiVA.org:uu-159876DiVA: diva2:447269
Available from: 2011-10-11 Created: 2011-10-11 Last updated: 2012-02-16Bibliographically approved
In thesis
1. On Constructive Sets and Partial Structures
Open this publication in new window or tab >>On Constructive Sets and Partial Structures
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The first three papers in this thesis study the formalisation of a set in type theory as a data type with an equivalence relation – an object usually known as a setoid. The corresponding formalisation of a locally small category is called an E-category.

In Paper I, we show that type theory without universes is insufficient for proving that some expected properties hold of the E-category of setoids, but that a minimal universe is sufficient.

In Paper II, we show that although the collection of all E-categories does not form a category, we can introduce a type-theoretic version of bicategories, and the E-categories form such an E-bicategory.

In Paper III, we consider the setoids inside a type-theoretic universe. The axiom of unique substitutions is proposed and used to show that these form a small category (that is, a category witha setoid of objects and a single setoid of all arrows). We demonstrate that this construction can not be carried out without adding some new axiom to type theory. We also show that the axiom of unique substitutions is strictly weaker than the axiom of unique identity proofs.

In Paper IV, we investigate partial equivalence relations, also known as partial setoids, in Heyting arithmetic in all finite types, and adapt the result that the extensional axiom of choice is equivalent to the combination of the intensional axiom of choice, classical logic, and an extensionality axiom.

In Paper V, we investigate PHL, a logic of partial terms, and prove a cut elimination theorem for it and for a related calculus.

Place, publisher, year, edition, pages
Uppsala: Department of Mathematics, 2011. 33 p.
Series
Uppsala Dissertations in Mathematics, ISSN 1401-2049 ; 74
National Category
Algebra and Logic
Research subject
Mathematical Logic
Identifiers
urn:nbn:se:uu:diva-160605 (URN)978-91-506-2245-4 (ISBN)
Public defence
2011-12-13, Polhemsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 13:15 (English)
Opponent
Supervisors
Available from: 2011-11-22 Created: 2011-10-27 Last updated: 2011-12-15Bibliographically approved

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