diff --git a/proposal/macros.tex b/proposal/macros.tex index 90d7382..604ae8b 100644 --- a/proposal/macros.tex +++ b/proposal/macros.tex @@ -4,6 +4,7 @@ \newcommand{\defeq}{\coloneqq} \newcommand{\bN}{\mathbb{N}} +\newcommand{\bC}{\mathbb{C}} \newcommand{\to}{\rightarrow}} \newcommand{\mto}{\mapsto}} \newcommand{\UU}{\ensuremath{\mathcal{U}}\xspace} @@ -12,3 +13,7 @@ \newcommand{\todo}[1]{\textit{#1}} \newcommand{\comp}{\circ} \newcommand{\x}{\times} +\newcommand{\Hom}{\mathit{Hom}} +\newcommand{\fmap}{\mathit{fmap}} +\newcommand{\idFun}{\mathit{id}} +\newcommand{\Sets}{\mathit{Sets}} diff --git a/proposal/proposal.tex b/proposal/proposal.tex index 679856c..61be25a 100644 --- a/proposal/proposal.tex +++ b/proposal/proposal.tex @@ -99,6 +99,26 @@ points. This is exactly the notion of equality of functions that we are interested in; that they are equal for all inputs. We call this \nomen{pointwise equality}, where the \emph{points} of a function refers to it's arguments. + +In the context of category theory the principle of functional extensionality is +for instance useful in the context of showing that representable functors are +indeed functors. The representable functor for a category $\bC$ and a fixed +object in $A \in \bC$ is defined to be: +% +\begin{align*} +\fmap \defeq X \mapsto \Hom_{\bC}(A, X) +\end{align*} +% +The proof obligation that this satisfies the identity law of functors +($\fmap\ \idFun \equiv \idFun$) becomes: +% +\begin{align*} +\Hom(A, \idFun_{\bX}) = (g \mapsto \idFun \comp g) \equiv \idFun_{\Sets} +\end{align*} +% +One needs functional extensionality to ``go under'' the function arrow and apply +the (left) identity law of the underlying category to proove $\idFun \comp g +\equiv g$ and thus closing the above proof. % \iffalse I also want to talk about: @@ -169,6 +189,15 @@ project will study and formalize this model. Note that I will \emph{not} aim to formalize CTT itself and therefore also not give the formal translation between the type theory and the meta-theory. Instead the translation will be accounted for informally. + +The project will formalize CwF's. It will also define what pieces of data are +needed for a model of CTT (without explicitly showing that it does in fact model +CTT). It will then show that a CwF gives rise to such a model. Furthermore I +will show that cubical sets are presheaf categories and that any presheaf +category is itself a CwF. This is the precise way by which the project aims to +provide a model of CTT. Note that this formalization specifcally does not +mention the language of CTT itself. Only be referencing this previous work do we +arrive at a model of CTT. % \section{Context} % @@ -230,7 +259,7 @@ assistant. One particular challenge in this context is that in a cubical setting there can be multiple distinct terms that inhabit a given equality proof.\footnote{This is -in contrast with ITT that enjoys \nomen{Uniqueness of identity proofs} +in contrast with ITT where one \emph{can} have \nomen{Uniqueness of identity proofs} (\cite[p. 4]{huber-2016}).} This means that the choice for a given equality proof can influence later proofs that refer back to said proof. This is new and relatively unexplored territory. @@ -240,8 +269,9 @@ basics of. So learning the necessary concepts from Category Theory will also be a goal and a challenge in itself. After this has been implemented it would also be possible to formalize Cubical -Type Theory and formally show that Cubical Sets are a model of this. This is not -a goal for this thesis but rather a natural extension of it. +Type Theory and formally show that Cubical Sets are a model of this. I do not +intend to formally implement the language of dependent type theory in this +project. The thesis shall conclude with a discussion about the benefits of Cubical Agda. %