We have seen how a view finder can be used for theory \emph{discovery} and finding constants with specific desired properties, but many other potential use cases are imaginable. The main problems to solve with respect to these is less about the algorithm or software design challenges, but user interfaces.

The theory discovery use case described in Sec. \ref{sec:usecase} is mostly desirable in a setting where a user is actively writing or editing a theory, so the integration in jEdit is sensible. However, the across-library use case in Sec. \ref{sec:pvs} already would be a lot more useful in a theory exploration setting, such as when browsing available archives on MathHub~\cite{mathhub} or in the graph viewer integrated in \mmt ~\cite{RupKohMue:fitgv17}. Additional specialized user interfaces would enable or improve the following use cases:

\end{newpart}

\begin{itemize}

\item\textbf{Model-/Countermodel Finding:} If the codomain of a morphism is a theory representing a specific model, it would tell her that those

are \emph{examples} of her abstract theory.

\item\textbf{Model-/Countermodel Finding:} If the codomain of a morphism is a theory representing a specific model, it would tell her that those are \emph{examples} of her abstract theory.

Furthermore, partial morphisms -- especially those that are total on some included theory -- could

be insightful \emph{counterexamples}.

Furthermore, partial morphisms -- especially those that are total on some included theory -- could be insightful \emph{counterexamples}.

\item\textbf{Library Refactoring:} Given that the view finder looks for \emph{partial} morphisms, we can use it to find natural

extensions of a starting theory. Imagine Jane removing the last of her axioms for ``beautiful sets'' --

the other axioms (disregarding finitude of her sets) would allow her to find e.g. both Matroids and

\emph{Ideals}, which would suggest to her to refactor her library accordingly.

\item\textbf{Library Refactoring:} Given that the view finder looks for \emph{partial} morphisms, we can use it to find natural extensions of a starting theory. Imagine Jane removing the last of her axioms for ``beautiful sets'' -- the other axioms (disregarding finitude of her sets) would allow her to find e.g. both Matroids and \emph{Ideals}, which would suggest to her to refactor her library accordingly.

Additionally, \emph{surjective} partial morphisms would inform her, that her theory would probably better

be refactored as an extension of the codomain, which would allow her to use all theorems and definitions

therein.

Additionally, \emph{surjective} partial morphisms would inform her, that her theory would probably better be refactored as an extension of the codomain, which would allow her to use all theorems and definitions therein.

\item\textbf{Theory Generalization:} If we additionally consider morphisms into and out of the theories found, this can make theory discovery even

more attractive. For example, a morphism from a theory of vector spaces intro matroids could inform Jane additionally,

that her beautiful sets, being matroids, form a generalization of the notion of linear independence in linear algebra.

\item\textbf{Folklore-based Conjecture:} If we were to keep book on our transfomations during preprocessing and normalization, we could use the found

morphisms for translating both into the codomain as well as back from there into our starting theory.

\item\textbf{Theory Generalization:} If we additionally consider morphisms into and out of the theories found, this can make theory discovery even more attractive. For example, a morphism from a theory of vector spaces intro matroids could inform Jane additionally, that her beautiful sets, being matroids, form a generalization of the notion of linear independence in linear algebra.

This would allow for e.g. discovering and importing theorems and useful definitions from some other library --

which on the basis of our encodings can be done directly by the view finder.

\item\textbf{Folklore-based Conjecture:} If we were to keep book on our transfomations during preprocessing and normalization, we could use the found morphisms for translating both into the codomain as well as back from there into our starting theory.

A useful interface might specifically prioritize morphisms into theories on top of which there are many

theorems and definitions that have been discovered.

This would allow for e.g. discovering and importing theorems and useful definitions from some other library -- which on the basis of our encodings can be done directly by the view finder.

A useful interface might specifically prioritize morphisms into theories on top of which there are many theorems and definitions that have been discovered.

\end{itemize}

For some of these use cases it would be advantageous to look for morphisms \emph{into} our working theory instead.

We will discuss some of our findings specifically regarding the PVS library as a case study.

\subsection{Normalization in PVS}\label{sec:normalizeinter}

PVS~\cite{pvs} is a proof assistant under active development, based on a higher-order logic with predicate subtyping and various convenience features such as record types, update expressions and inductive datatypes. In addition to the \emph{Prelude} library, which contains the most common domains of mathematical discourse and is shipped with PVS itself, there is a large library of formal mathematics developed and maintained by NASA~\cite{PVSlibraries:url}.

PVS~\cite{pvs} is a proof assistant under active development, based on a higher-order logic with predicate subtyping and various convenience features such as record types, update expressions and inductive datatypes. In addition to the \emph{Prelude} library, which contains the most common domains of mathematical discourse and is shipped with PVS itself, there is a large library of formal mathematics developed and maintained by NASA~\cite{PVSlibraries:on}.

\paragraph{} While features like subtyping and records are interesting challenges, we will concentrate on one specific idiosyncrasy in PVS -- its prevalent use of \emph{theory parameters}.