Semi-simplicial Types in Logic-enriched Homotopy Type Theory

The problem of defining Semi-Simplicial Types (SSTs) in Homotopy Type Theory (HoTT) has been recognized as important during the Year of Univalent Foundations at the Institute of Advanced Study. According to the interpretation of HoTT in Quillen model categories, SSTs are type-theoretic versions of Reedy fibrant semi-simplicial objects in a model category and simplicial and semi-simplicial objects play a crucial role in many constructions in homotopy theory and higher category theory. Attempts to define SSTs in HoTT lead to some difficulties such as the need of infinitary assumptions which are beyond HoTT with only non-strict equality types. Voevodsky proposed a definition of SSTs in Homotopy Type System (HTS), an extension of HoTT with non-fibrant types, including an extensional strict equality type. However, HTS does not have the desirable computational properties such as decidability of type checking and strong normalization. In this paper, we study a logic-enriched homotopy type theory, an alternative extension of HoTT with equational logic based on the idea of logic-enriched type theories. In contrast to Voevodskys HTS, all types in our system are fibrant and it can be implemented in existing proof assistants. We show how SSTs can be defined in our system and outline an implementation in the proof assistant Plastic

Classical Predicative Logic-Enriched Type Theories

A logic-enriched type theory (LTT) is a type theory extended with a primitive mechanism for forming and proving propositions. We construct two LTTs, named LTTO and LTTO*, which we claim correspond closely to the classical predicative systems of second order arithmetic ACAO and ACA. We justify this claim by translating each second-order system into the corresponding LTT, and proving that these translations are conservative. This is part of an ongoing research project to investigate how LTTs may be used to formalise different approaches to the foundations of mathematics. The two LTTs we construct are subsystems of the logic-enriched type theory LTTW, which is intended to formalise the classical predicative foundation presented by Herman Weyl in his monograph Das Kontinuum. The system ACAO has also been claimed to correspond to Weyl's foundation. By casting ACAO and ACA as LTTs, we are able to compare them with LTTW. It is a consequence of the work in this paper that LTTW is strictly stronger than ACAO. The conservativity proof makes use of a novel technique for proving one LTT conservative over another, involving defining an interpretation of the stronger system out of the expressions of the weaker. This technique should be applicable in a wide variety of different cases outside the present work.Comment: 49 pages. Accepted for publication in special edition of Annals of Pure and Applied Logic on Computation in Classical Logic. v2: Minor mistakes correcte

A THERMAL MODEL FOR IGBT MODULES AND ITS IMPLEMENTATION IN A REAL TIME SIMULATOR

As the power density and switching frequency increase, thermal analysis of power electronics system becomes imperative. The analysis provides valuable information on the semiconductor rating, long-term reliability and efficient heat-sink design. The aim of this thesis is to build a comprehensive thermal model for the power IGBT modules used in three-phase inverters in order to predict the dynamic junction temperature rise under real operating conditions. The thermal model is developed in two steps: first, the losses are calculated and then the junction temperature is estimated. The real-time simulation environment dictates the requirements for the models: easy implementation on the software platform SIMULINK and fast calculation time. The power losses model, which is based on the look-up table method for calculating the conduction and switching losses, are successfully built and implemented in the real time simulation environment. The power losses equations are derived from the experimental data. Several algorithms are developed to catch every switching event and to solve the synchronization problem in a real-time system. An equivalent RC network model is built to perform the thermal analysis. The parameters of the thermal network are extracted from the junction to case and case to ambient dynamic thermal impedance curves. Two separate approaches are followed in deriving these thermal characteristic curves. The first approach uses the experimental data available while the second approach uses the commercial software package ANSYS. The 3-D simulation results using ANSYS agree well with the experimental data and therefore can be relied upon to extract the parameters of the thermal RC network. The latter is successfully implemented using the transfer function method, and is then built in SIMULINK environment for the use in a real time simulator. The power losses and thermal RC network models are extensively tested in a real time simulator environment. The accuracy of the models is confirmed by comparing their predictions with the experimental data

Individuation Criteria, Dot-types and Copredication:A View from Modern Type Theories

International audienceIn this paper we revisit the issue of copredica-tion from the perspective of modern type theories. Specifically, we look at: a) the counting properties of dot-types, and b) the case of a complex dot-type that has remained unsolved in the literature, i.e. that of newspaper. As regards a), we show that the account proposed in (Luo, 2010) for dot-types makes the correct predictions as regards counting. In order to verify this, we implement the account in the Coq proof-assistant and check that the desired inferences follow. Then, we look at the case of b), the case of a dot-type which is both resource and context sensitive. We propose a further resource sensitive version of the dot-type, in effect a linear dot-type. This along with local coercions can account for the behaviour attested

Subtype Universes

We introduce a new concept called a subtype universe, which is a collection of subtypes of a particular type. Amongst other things, subtype universes can model bounded quantification without undecidability. Subtype universes have applications in programming, formalisation and natural language semantics. Our construction builds on coercive subtyping, a system of subtyping that preserves canonicity. We prove Strong Normalisation, Subject Reduction and Logical Consistency for our system via transfer from its parent system UTT[?]. We discuss the interaction between subtype universes and other sorts of universe and compare our construction to previous work on Power types

A Metatheoretic Analysis of Subtype Universes

Subtype universes were initially introduced as an expressive mechanisation of bounded quantification extending a modern type theory. In this paper, we consider a dependent type theory equipped with coercive subtyping and a generalisation of subtype universes. We prove results regarding the metatheoretic properties of subtype universes, such as consistency and strong normalisation. We analyse the causes of undecidability in bounded quantification, and discuss how coherency impacts the metatheoretic properties of theories implementing bounded quantification. We describe the effects of certain choices of subtyping inference rules on the expressiveness of a type theory, and examine various applications in natural language semantics, programming languages, and mathematics formalisation