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doc/abstract.tex
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doc/abstract.tex
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\chapter*{Abstract}
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The usual notion of propositional equality in intensional type-theory is
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restrictive. For instance it does not admit functional extensionality or
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univalence. This poses a severe limitation on both what is \emph{provable} and
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the \emph{re-usability} of proofs. Recent developments have, however, resulted
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in cubical type theory which permits a constructive proof of these two important
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notions. The programming language Agda has been extended with capabilities for
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working in such a cubical setting. This thesis will explore the usefulness of
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this extension in the context of category theory.
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The thesis will motivate and explain why propositional equality in cubical Agda
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is more expressive than in standard Agda. Alternative approaches to Cubical Agda
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will be presented and their pros and cons will be explained. It will emphasize
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why it is useful to have a constructive interpretation of univalence. As an
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example of this two formulations of monads will be presented: Namely monaeds in
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the monoidal form an monads in the Kleisli form.
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Finally the thesis will explain the challenges that a developer will face when
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working with cubical Agda and give some techniques to overcome these
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difficulties. It will also try to suggest how furhter work can help allievate
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some of these challenges.
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\chapter{Introduction}
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\chapter{Introduction}
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Functional extensionality and univalence is not expressible in
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\nomen{Intensional Martin Löf Type Theory} (ITT). This poses a severe limitation
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on both what is \emph{provable} and the \emph{re-usability} of proofs. Recent
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developments have, however, resulted in \nomen{Cubical Type Theory} (CTT) which
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permits a constructive proof of these two important notions.
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Furthermore an extension has been implemented for the proof assistant Agda
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(\cite{agda}, \cite{cubical-agda}) that allows us to work in such a ``cubical
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setting''. This thesis will explore the usefulness of this extension in the
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context of category theory.
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\section{Motivating examples}
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\section{Motivating examples}
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In the following two sections I present two examples that illustrate some
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In the following two sections I present two examples that illustrate some
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limitations inherent in ITT and -- by extension -- Agda.
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limitations inherent in ITT and -- by extension -- Agda.
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%
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%
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\subsection{Functional extensionality}
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\subsection{Functional extensionality}
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\label{sec:functional-extensionality}
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\label{sec:functional-extensionality}%
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Consider the functions:
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Consider the functions:
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%
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%
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\begin{multicols}{2}
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\begin{multicols}{2}
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@ -30,11 +19,10 @@ Consider the functions:
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\end{multicols}
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\end{multicols}
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%
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%
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$n + 0$ is \nomen{definitionally} equal to $n$, which we write as $n + 0 = n$.
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$n + 0$ is \nomen{definitionally} equal to $n$, which we write as $n + 0 = n$.
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This is also \called \nomen{judgmental} equality. We call it definitional
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This is also called \nomen{judgmental} equality. We call it definitional
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equality because the \emph{equality} arises from the \emph{definition} of $+$
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equality because the \emph{equality} arises from the \emph{definition} of $+$
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which is:
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which is:
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%
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%
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\newcommand{\suc}[1]{\mathit{suc}\ #1}
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\begin{align*}
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\begin{align*}
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+ & \tp \bN \to \bN \to \bN \\
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+ & \tp \bN \to \bN \to \bN \\
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n + 0 & \defeq n \\
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n + 0 & \defeq n \\
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@ -91,3 +91,4 @@
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\newcommand\Endo[1]{\varindex{Endo}\ #1}
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\newcommand\Endo[1]{\varindex{Endo}\ #1}
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\newcommand\EndoR{\mathcal{R}}
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\newcommand\EndoR{\mathcal{R}}
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\newcommand\funExt{\varindex{funExt}}
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\newcommand\funExt{\varindex{funExt}}
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\newcommand{\suc}[1]{\mathit{suc}\ #1}
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@ -48,7 +48,7 @@
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\frontmatter
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\frontmatter
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\myfrontmatter
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\myfrontmatter
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\maketitle
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\maketitle
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\addtocontents{toc}{\protect\thispagestyle{empty}}
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\input{abstract.tex}
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\tableofcontents
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\tableofcontents
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\mainmatter
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\mainmatter
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%
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%
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