获取页面中环境的开始和结束计数器

Question

您需要使用标记来解决这个问题。这是一个简单的解决方案。它使用包extramarks。它不会在第一个定理之前打印标题。使用旧版本（版本 4 或更早版本）extramarks有时会与由部分生成的标记发生不必要的交互（不在以下示例中）。在这种情况下，您应该使用extramarks版本 5（下面的链接）。

我不喜欢在很多页面的页眉中都显示“定理 xx”，而这个定理比这个定理早几页。为此，我还给出了第二个更复杂的解决方案，即只有当页面上确实存在（部分）定理时才打印页眉。任你选择。

解决方案 1

\documentclass[12pt]{book}
\usepackage{fancyhdr,lipsum,blindtext,amsthm}
\usepackage{extramarks}
\usepackage{ifthen}
% If you want to number theorems within chapters, add '[chapter]'
\newtheorem{theorem}{Theorem}
% We add a new mark containing the theorem number at the beginning of a
% theorem. As the theorem number hasn't been incremented yet at the
% beginning, we increment it first, set the mark and then decrement the
% theorem number.
\AtBeginEnvironment{theorem}{\addtocounter{theorem}{1}%
  \extramarks{\thetheorem}{}\addtocounter{theorem}{-1}}

\renewcommand{\chaptermark}[1]{\markboth{#1}{#1}}
\fancypagestyle{fancy}{
    \fancyhf{}
    \fancyhead[LE]{\thepage}
    \fancyhead[C]{\ifthenelse{0\firstleftxmark=0}
      {}% no theorems yet, so no header
      {\textsc{Theorem} \ifthenelse{\equal{\firstleftxmark}{\lastleftxmark}}
          {\firstleftxmark}% Only one theorem on the page
          {\firstleftxmark–\lastleftxmark}}}% Multiple theorems on the page
    %\renewcommand{\headrulewidth}{0pt}
    \renewcommand{\footrulewidth}{0pt}
}
\setlength{\headheight}{15pt}

\begin{document}
    \pagestyle{plain} % This avoids a bug in extramarks - may also be headings
    \tableofcontents
    \pagenumbering{arabic}
    \clearpage
    \pagestyle{fancy}
    %\addcontentsline{toc}{part}{\protect\centering{}Chapter I}
    \part{One}
    \chapter{The Greatest Common Divisor of Two Numbers}
    \lipsum
    \begin{theorem}
      one        
    \end{theorem}

    Some text

    \begin{theorem}
      two
    \end{theorem}
    \newpage

    \begin{theorem}
      three
    \end{theorem}

    \blinddocument
    \section{Section of first}
    \section{Another Section of First}
    \part{Two}
    \chapter*{Unnumbered Chapter}
    \lipsum
    \chapter{Prime Numbers and Factorization into Prime Factors}
    \section*{Unnumbered Section}
    \lipsum
    \begin{theorem}
      three
    \end{theorem}
    \section{Test Section}
    \begin{theorem}
      four
    \end{theorem}
    \begin{theorem}
      five
    \end{theorem}
    \begin{theorem}
      This is a multi-page theorem. \\
      \lipsum
    \end{theorem}
\end{document}

解决方案 2

此解决方案需要extramarks版本 5，可在以下位置找到 https://github.com/pietvo/fancyhdr/tree/5.0beta

仅当页面上确实存在（部分）定理时，此解决方案才会打印标题。

\documentclass[12pt]{book}
\usepackage{fancyhdr,lipsum,blindtext,amsthm}
\usepackage{extramarks} % Need version 5
\usepackage{ifthen}
% If you want to number theorems within chapters, add '[chapter]'
\newtheorem{theorem}{Theorem}
% We add two new marks at the beginning and the end of a theorem.
% The left one has the theorem number. As the theorem number hasn't been
% incremented yet at the beginning, we increment it first, set the mark
% and then decrement the theorem number. We need this mark both at the
% beginning and the end, so that we can use the number on both pages if
% a theorem crosses a page boundary
% The right mark is 1 at the beginning and 0 at the end of a theorem.
% This allows us to check if we are inside a multipage theorem.
\AtBeginEnvironment{theorem}{\addtocounter{theorem}{1}%
  \extramarks{\thetheorem}{1}\addtocounter{theorem}{-1}}
\AtEndEnvironment{theorem}{\extramarks{\thetheorem}{0}}

\renewcommand{\chaptermark}[1]{\markboth{#1}{#1}}
\fancypagestyle{fancy}{
    \fancyhf{}
    \fancyhead[LE]{\thepage}
    \fancyhead[C]{\ifextramarksmissing{left} % no theorem marks on this page
        % Check if we are in the middle of a multipage theorem
        {\ifthenelse{\equal{\firstrightxmark}{1}}{\textsc{Theorem} \firstleftxmark}{}}
        {\textsc{Theorem} \ifthenelse{\equal{\firstleftxmark}{\lastleftxmark}}
          {\firstleftxmark} % Only one theorem on the page
          {\firstleftxmark–\lastleftxmark}}} % Multiple theorems on the page
    %\renewcommand{\headrulewidth}{0pt}
    \renewcommand{\footrulewidth}{0pt}
}
\setlength{\headheight}{15pt}

\begin{document}
    \tableofcontents
    \pagenumbering{arabic}
    \clearpage
    \pagestyle{fancy}
    %\addcontentsline{toc}{part}{\protect\centering{}Chapter I}
    \part{One}
    \chapter{The Greatest Common Divisor of Two Numbers}
    \lipsum
    \begin{theorem}
      one        
    \end{theorem}

    Some text

    \begin{theorem}
      two
    \end{theorem}
    \newpage

    \begin{theorem}
      three
    \end{theorem}

    \blinddocument
    \section{Section of first}
    \section{Another Section of First}
    \part{Two}
    \chapter*{Unnumbered Chapter}
    \lipsum
    \chapter{Prime Numbers and Factorization into Prime Factors}
    \section*{Unnumbered Section}
    \lipsum
    \begin{theorem}
      three
    \end{theorem}
    \section{Test Section}
    \begin{theorem}
      four
    \end{theorem}
    \begin{theorem}
      five
    \end{theorem}
    \begin{theorem}
      This is a multi-page theorem. \\
      \lipsum
    \end{theorem}
\end{document}

Answer 1