Line break in starred ntheorem header

Question

I came across this question that was posted before and have been using the solution for a while. However, I can't seem to get the same thing to work with starred environments.

I am aware that long theorem titles have been a long-standing bug with ntheorem. However, some pointers as to how I can workaround this, if there exists one such workaround out there, is appreciated.

The following is a MWE using the tufte class, just to stay consistent with my usual setup.

\documentclass{tufte-book}
\usepackage{etoolbox}
\usepackage{ntheorem}

% Workaround for long titles in ntheorem
\makeatletter
\let\nobreakitem\item
\let\@nobreakitem\@item
\patchcmd{\nobreakitem}{\@item}{\@nobreakitem}{}{}
\patchcmd{\nobreakitem}{\@item}{\@nobreakitem}{}{}
\patchcmd{\@nobreakitem}{\@itempenalty}{\@M}{}{}
\patchcmd{\@xthm}{\ignorespaces}{\nobreak\ignorespaces}{}{}
\patchcmd{\@ythm}{\ignorespaces}{\nobreak\ignorespaces}{}{}

\renewtheoremstyle{break}%
  {\item{\theorem@headerfont
          ##1\ ##2\theorem@separator}\hskip\labelsep\relax\nobreakitem}%
  {\item{\theorem@headerfont
          ##1\ ##2\ (##3)\theorem@separator}\hskip\labelsep\relax\nobreakitem}
\makeatother

\theoremstyle{break}
\theoremprework{\textcolor{magenta}{\hrule height 2pt width \textwidth}}
\theoremheaderfont{\color{magenta}\normalfont\bfseries}
\theorempostwork{\textcolor{magenta}{\hrule height 2pt width \textwidth}}
\theoremindent10pt
\newtheorem{theorem}{Theorem}

\theoremprework{\textcolor{magenta}{\hrule height 2pt width \textwidth}}
\theoremheaderfont{\color{magenta}\normalfont\bfseries}
\theorempostwork{\textcolor{magenta}{\hrule height 2pt width \textwidth}}
\theoremindent10pt
\newtheorem*{theoremn}{Theorem}

\begin{document}
\begin{theorem}[Theorem Theorem Theorem Theorem Theorem Theorem Theorem Theorem Theorem Theorem Theorem Theorem Theorem Theorem Theorem Theorem]
  This is a numbered theorem.
\end{theorem}

\begin{theoremn}[Theorem Theorem Theorem Theorem Theorem Theorem Theorem Theorem Theorem Theorem Theorem Theorem Theorem Theorem Theorem Theorem]
  This is an unnumbered theorem.
\end{theoremn}
\end{document}

The following is an image of how it looks like:

For those who intend to recommend amsthm, note that I cannot achieve the styling of theorem environments that I can do with ntheorem, which is why I would prefer to find a solution with ntheorem, rather than dropping it. Also, the use of frames (e.g. mdframed) is a no-go, since I am also using the tufte class, and I greatly rely on having ample side notes and margin notes in my documents.

Was not sure how helpful it would be, especially since it is very similar to the linked problem, but I have added an MWE anyway. — Japorized, May 14 '19 at 22:33

score 2 · Accepted Answer · answered May 14 '19 at 23:18

You can add

\def\thm@nonumberbreak{%
  \def\@begintheorem##1##2{%
    \item
    {\theorem@headerfont##1\theorem@separator}
    \hskip\labelsep\relax\nobreakitem 
  }%
  \def\@opargbegintheorem##1##2##3{%
    \item 
    {\theorem@headerfont##1\ (##3)\theorem@separator}%
    \hskip\labelsep\relax\nobreakitem 
  }%
}

before \makeatother. More simply, use regexpatch instead of etoolbox.

\documentclass{tufte-book}
\usepackage{regexpatch}
\usepackage{ntheorem}

% Workaround for long titles in ntheorem
\makeatletter
\let\nobreakitem\item
\let\@nobreakitem\@item
\xpatchcmd{\nobreakitem}{\@item}{\@nobreakitem}{}{}
\xpatchcmd{\nobreakitem}{\@item}{\@nobreakitem}{}{}
\xpatchcmd{\@nobreakitem}{\@itempenalty}{\@M}{}{}
\xpatchcmd{\@xthm}{\ignorespaces}{\nobreak\ignorespaces}{}{}
\xpatchcmd{\@ythm}{\ignorespaces}{\nobreak\ignorespaces}{}{}

\renewtheoremstyle{break}%
  {\item{\theorem@headerfont
          ##1\ ##2\theorem@separator}\hskip\labelsep\relax\nobreakitem}%
  {\item{\theorem@headerfont
          ##1\ ##2\ (##3)\theorem@separator}\hskip\labelsep\relax\nobreakitem}
% make \th@nonumberbreak the same as \th@break, but remove "\ ##2"
\let\th@nonumberbreak\th@break
\xpatchcmd*{\th@nonumberbreak}{\ ##2}{}{}{}
\makeatother

\theoremstyle{break}
\theoremprework{\textcolor{magenta}{\hrule height 2pt width \textwidth}}
\theoremheaderfont{\color{magenta}\normalfont\bfseries}
\theorempostwork{\textcolor{magenta}{\hrule height 2pt width \textwidth}}
\theoremindent10pt
\newtheorem{theorem}{Theorem}

\theoremprework{\textcolor{magenta}{\hrule height 2pt width \textwidth}}
\theoremheaderfont{\color{magenta}\normalfont\bfseries}
\theorempostwork{\textcolor{magenta}{\hrule height 2pt width \textwidth}}
\theoremindent10pt
\newtheorem*{theoremn}{Theorem}

\begin{document}
\begin{theorem}[Theorem Theorem Theorem Theorem Theorem Theorem Theorem Theorem Theorem Theorem Theorem Theorem Theorem Theorem Theorem Theorem]
  This is a numbered theorem.
\end{theorem}

\begin{theoremn}[Theorem Theorem Theorem Theorem Theorem Theorem Theorem Theorem Theorem Theorem Theorem Theorem Theorem Theorem Theorem Theorem]
  This is an unnumbered theorem.
\end{theoremn}
\end{document}

Thank you. How does one go about learning how to tackle these problems on their own? Mind sharing some of your insight to help a learning fellow? I am aware that this is not the best place for these sort of questions but I am out of my wit. — Japorized, May 15 '19 at 02:31
@Japorized I just noticed a bunch of \vbox and \hbox in the definition of \th@nonumberbreak; then I looked at \th@break and thought that it ought to be similar. I never use ntheorem because it's rather inflexible. — egreg, May 15 '19 at 08:46

Line break in starred ntheorem header

1 Answers1