Making a cleveref String Lowercase

Question

I'm using cleveref to cross-reference my theorems throughout my document. However, since certain theorems are so popular, I much prefer to refer to them by names as opposed to their theorem numbers; but I would still like them to be clickable, so that clicking on a theorem's name, wherever it's mentioned, will take you straight to it.

To create custom string, I implemented the solution provided by this answer, which can be shown in the MWE below.

\documentclass{article}
\usepackage{amsthm, parskip, hyperref, cleveref}

% Theorems
\theoremstyle{definition}
\newtheorem{theorem}{Theorem}[section]
\newtheorem{example}[theorem]{Example}

% Solution from https://tex.stackexchange.com/a/109864/78913
\makeatletter
\newcommand{\myref}[1]{\cref{#1}\mynameref{#1}{\csname r@#1\endcsname}}
\newcommand{\Myref}[1]{\Cref{#1}\mynameref{#1}{\csname r@#1\endcsname}}

\def\mynameref#1#2{%
    \begingroup
    \edef\@mytxt{#2}%
    \edef\@mytst{\expandafter\@thirdoffive\@mytxt}%
    \ifx\@mytst\empty\else
    \space(\nameref{#1})\fi
    \endgroup
}
\makeatother

\begin{document}
    \section{Group Actions}

    \begin{theorem}[Orbit-Stabiliser Theorem]
        \label{thm:ost}
        Let $G$ be a finite group acting on a finite set $X$. Then 
        \[|G| = \mathop{\mathrm{Orb}}(x) \times \mathop{\mathrm{Stab}}(x).\]
    \end{theorem}

    \begin{example}
        Let $G$ act on $X$, where $|G| = 55$ and $|X| = 18$. Show that the action has at least two fixed points.

        By the \nameref{thm:ost}, ...
    \end{example}

\end{document}

This code provides the following output:

Is there a way I can change the label so that the text is in lower-case? I tried using \MakeLowercase{}, but this didn't work. And is there a way I can modify the label in general? If I have something like "Cauchy's Theorem" for example, I'd like to have it appear as "Cauchy's theorem" in text, with a lower-case t.

I appreciate any assistance.

Answer 1

You're going to have to tell LaTeX explicitly how you want the theorem name capitalised. There's no way to automatically detect which words are proper nouns like "Cauchy" that should stay capitalised.

Referring to things by name falls more within the remit of the nameref package. Cleveref is concerned with referring to things by their label. But since you'll have to specify the correctly-capitalised theorem name explicitly anyway, there is a way to do it with just cleveref without much extra effort:

\documentclass{article}
\usepackage{amsthm, parskip, hyperref, cleveref}

% Theorems
\theoremstyle{definition}
\newtheorem{theorem}{Theorem}[section]
\newtheorem{example}[theorem]{Example}

\begin{document}
    \section{Group Actions}

    \begin{theorem}[Orbit-Stabiliser Theorem]
      \label{thm:ostnum}
      \label[ost]{thm:ostname}
      \crefformat{ost}{#2orbit-stabiliser theorem#3}
      \Crefformat{ost}{#2Orbit-stabiliser theorem#3}
      Let $G$ be a finite group acting on a finite set $X$. Then
      \[|G| = \mathop{\mathrm{Orb}}(x) \times \mathop{\mathrm{Stab}}(x).\]
    \end{theorem}

    \begin{example}
        Let $G$ act on $X$, where $|G| = 55$ and $|X| = 18$. Show that the action has at least two fixed points.

        By the \cref{thm:ostname}, which is given in \cref{thm:ostnum}, \dots
    \end{example}

\end{document}

This works by defining a new cross-reference type ost, and telling cleveref to format references to it using the correctly capitalised theorem name. The additional thm:ostnum label is just to demonstrate how you can still refer to the theorem by its label too, if desired.

If you want to do this often, it could be tidied up a bit by bundling the \label, \crefformat, \Crefformat and maybe even the theorem definition into a new macro or environment.

Answer 2

I've written the crossreftools package some weeks ago (it's available on CTAN, TeXLive and MikTeX, current version is 0.4), which provides expandable extraction of the cross-reference information stored by hyperref and cleveref.

\MakeLowercase won't work with \nameref, since \nameref isn't expandable, so the name information has to be extracted first, then apply \MakeLowercase.

The name reference is done with \crtrefname, but this would not provide a hyperlink, which would make the whole issue unexpandable again. The hyper anchor can be extracted with \crtrefanchor, together with a \hyperlink wrapped in a new command, say \lowernameref this will give the lower case title.

Please note, that \lowernameref is unexpandable of course.

\documentclass{article}
\usepackage{amsthm, parskip, hyperref, cleveref}

\usepackage{crossreftools}

% Theorems
\theoremstyle{definition}
\newtheorem{theorem}{Theorem}[section]
\newtheorem{example}[theorem]{Example}

% Solution from https://tex.stackexchange.com/a/109864/78913
\makeatletter
\newcommand{\myref}[1]{\cref{#1}\mynameref{#1}{\csname r@#1\endcsname}}
\newcommand{\Myref}[1]{\Cref{#1}\mynameref{#1}{\csname r@#1\endcsname}}

\newcommand{\lowernameref}[1]{\hyperlink{\crtrefanchor{#1}}{\MakeLowercase{\crtrefname{#1}}}}


\def\mynameref#1#2{%
    \begingroup
    \edef\@mytxt{#2}%
    \edef\@mytst{\expandafter\@thirdoffive\@mytxt}%
    \ifx\@mytst\empty\else
    \space(\nameref{#1})\fi
    \endgroup
}
\makeatother

\begin{document}
    \section{Group Actions}

    \begin{theorem}[Orbit-Stabiliser Theorem]
        \label{thm:ost}
        Let $G$ be a finite group acting on a finite set $X$. Then 
        \[|G| = \mathop{\mathrm{Orb}}(x) \times \mathop{\mathrm{Stab}}(x).\]
    \end{theorem}

    \begin{example}
        Let $G$ act on $X$, where $|G| = 55$ and $|X| = 18$. Show that the action has at least two fixed points.

        By the \lowernameref{thm:ost}, ...
    \end{example}

\end{document}