[Tex/LaTex] Reference undefined in \section with amsbook

amsbookcross-referencingheader-footersectioning

I have a section that is devoted to the proof of a theorem, and hence I used

\section{Proof of Theorem~\ref{thm}}

Of course, because of the headers that are capitalized, it asks for \ref{THM} when producing the header, and I get an obvious error. What is the proper way to handle such a case? Below is a MWE:

\documentclass{amsbook}
\usepackage{lipsum}
\newtheorem{thm}{Theorem}
\begin{document}
\chapter{First Chapter}
\section{The Theorem}
\begin{thm}[Lipsum Theorem]
\label{thm}
\lipsum[1]
\end{thm}
\section{Proof of Theorem~\ref{thm}}
\lipsum[1-23]
\end{document}

When compiling I get:

LaTeX Warning: Reference `THM' on page 3 undefined on input line 14.

(each time it produces a header), and the header shows

`2. PROOF OF THEOREM ??'

Best Answer

If you don't feel like hacking around and don't mind just circumventing your problem: a theorem can have multiple labels, so give it \label{THM} as well.

Related Solutions

[Tex/LaTex] Using the amsbook Class

There are several questions here.

You can define a new page style to change the header format. In my example code this is done defining \ps@spheadings.

You can define a new theorem style to change the format for the theorem-like structures. In my example code this is done defining \th@spplain.I defined this new style using low-level commands, but you could use the features provided by the amsthm package.

\documentclass{amsbook}
\usepackage{lipsum}

\makeatletter
\def\ps@spheadings{\ps@empty
  \def\@evenhead{\normalfont\scriptsize
      \rlap{\thepage}\hfil \leftmark{}{}}%
  \def\@oddhead{\normalfont\scriptsize
      \rightmark{}{}\hfil \llap{\thepage}}%
  \let\@mkboth\markboth
  \def\partmark{\@secmark\markboth\partrunhead\partname}%
  \def\chaptermark{%
    \@secmark\markboth\chapterrunhead{}}%
  \def\sectionmark{%
    \@secmark\markright\sectionrunhead\sectionname}%
}
\def\th@spplain{%
  \let\thm@indent\relax
  \thm@headfont{\bfseries}% heading font bold face
  \let\thmhead\thmhead@plain \let\swappedhead\swappedhead@plain
  \thm@preskip.5\baselineskip\@plus.2\baselineskip
                                    \@minus.2\baselineskip
  \thm@postskip\thm@preskip
  \normalfont
}
\makeatother

\theoremstyle{spplain}
\newtheorem{theo}{Theorem}

\pagestyle{spheadings}

\begin{document}

\chapter{A test chapter}
\section{A test section}
\begin{theo}
\lipsum[1]
\end{theo}
\lipsum[1-30]

\end{document}

Although both modifications are not difficult to achieve, you should think carefully if amsbook is really the best class for you, or if perhaps some other class would suit you better.

To customize the theorem-like structures, you can use the amsthm package (I already provided the link); the ntheorem package could also be a possibility if your document class is not from the AMS collection.

If you decide not to use the amsbook document class, but to use some of the standard document classes, then you can customize the headers using either the fancyhdr or the titlesec packages.

In What are the available “documentclass” types and their uses? you can find a description of some of the available document classes; besides amsbook, and book, the document classes scrbook and memoir could be an option for you.

Here's a simple schematic document showing titlesec and amsthm in action with the book document class:

\documentclass[twoside]{book}
\usepackage{amsthm}
\usepackage[pagestyles]{titlesec}
\usepackage{lipsum}

\newpagestyle{mystyle}{
 \sethead[left-odd][center-odd][right-odd]{left-even}{center-even}{right-odd}
  \setfoot[left-odd][center-odd][right-odd]{left-even}{center-even}{right-odd}
}

\newtheoremstyle{mystyle}
{3pt}% ⟨Space above⟩
{3pt}% ⟨Space below⟩
{\normalfont}% ⟨Body font⟩
{}% ⟨Indent amount⟩
{\bfseries}% ⟨Theorem head font⟩
{.}% ⟨Punctuation after theorem head⟩
{.5em}% ⟨Space after theorem head⟩
{}% ⟨Theorem head spec (can be left empty, meaning ‘normal’)⟩
\theoremstyle{mystyle}
\newtheorem{theo}{Theorem}

\pagestyle{mystyle}

\begin{document}

\chapter{A test chapter}
\section{A test section}
\begin{theo}
\lipsum[1]
\end{theo}
\lipsum[1-30]

\end{document}

[Tex/LaTex] Page headers in uppercase (amsbook+chapterbib+natbib)

well, i've figured out why chapterbib causes the running heads to be uncapitalized.

amsbook depends on these definition for all running heads:

\def\partrunhead#1#2#3{%
  \@ifnotempty{#2}{\uppercase{\ignorespaces#1 #2\unskip}\@ifnotempty{#3}{. }}%
  \def\@tempa{#3}%
  \ifx\@empty\@tempa\else
    \begingroup \def\\{ \ignorespaces}% defend against questionable usage
    \uppercasenonmath\@tempa\@tempa
    \endgroup
  \fi
}
\let\chapterrunhead\partrunhead
\let\sectionrunhead\partrunhead

notice where the \uppercasenonmath is applied. the relevant marks are produced from #3 in this process.

chapterbib redefines the way these marks are set, as

 \csname#2mark\endcsname{\bibname}

buried deep within the definition of \sectionbib (which defines the behavior for a chapter as well as for a section) so in effect the amsbook definition isn't applied at all (for the bibliography) when chapterbib is used.

it looks like the most expedient way to get uppercased running heads for the references is to intervene after \begin{thebibliography} (in the .bbl file). your code

\markboth{\MakeUppercase{\bibname}}{\MakeUppercase{\bibname}}

will work as intended there.

an alternative approach would be to get rid of uppercasing entirely, by redefining \partrunhead to omit \uppercasenonmath and then reiterating the two \let statements.

i haven't investigated whether natbib.sty redefines how the running heads are set, but it probably does.

Best Answer

Related Solutions

[Tex/LaTex] Using the amsbook Class

[Tex/LaTex] Page headers in uppercase (amsbook+chapterbib+natbib)

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