I want to use the \mathsection in the chapter content, as I said and Gonzalo Medina figured out for me in Using \mathsection in the chapter.

However, when I use his solution, the Table of Contents went wrong like this:

Here is the code of my template :

 \documentclass[11pt,a4paper]{amsbook}
\usepackage{bbold,amscd,amsmath,amssymb,amsfonts,ifthen,amsthm}
\usepackage[utf8]{vietnam}
\usepackage{titlesec}
\usepackage[all]{xypic}
\usepackage{kpfonts}
%%%%% FOR SEARCHING LABELS AND REFS %%%%%%%%%%%%%%%
\usepackage{color}
\usepackage[color,notref,notcite]{showkeys}
\definecolor{refkey}{rgb}{0,0,0}
\definecolor{labelkey}{rgb}{0,0,1}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\usepackage{newcent}
%\usepackage[unicode]{hyperref}
\usepackage{cmap}

%%%%%MARGIN %%%%%%%%%%%%%%%%%%%
\oddsidemargin 2cm %0.3cm
\evensidemargin 2cm % 3cm
\topmargin2cm
\textwidth12cm %15
\textheight18.5cm %22
\topskip3ex
%% FOR TYPESETTING VIETNAMESE WITH AMSART %%%%%%
\def\firstofone#1{#1}
\let\uppercase\firstofone
\let\MakeUppercase\firstofone
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

%STYLE%%%%%%%%%%%
\def\thepart{\Roman{part}}
\def\thechapter{\arabic{chapter}}
\def\thesection{\arabic{section}}
\def\labelenumi{\roman{enumi})}
%\numberwithin{thm}{section}
\numberwithin{equation}{section}
\titleformat{\chapter}[display]
{\normalfont\huge\filcenter\scshape}{\chaptertitlename\ \thechapter}{0.2pt}{}
\titleformat{\section}
{\normalfont\Large\bfseries}{\S\thesection.}{0.1em}{}

%THEOREM%%%%%%%%%%%%%%%%
\theoremstyle{plain}
\newtheorem{thm}{Theorem}[section]
\newtheorem{dl}[thm]{Định lý}
\newtheorem{bd}[thm]{Bổ đề}
\newtheorem{hq}[thm]{Hệ quả}
\newtheorem{md}[thm]{Mệnh đề}
\theoremstyle{definition}
\newtheorem{nx}[thm]{Nhận xét}
\newtheorem{chuy}[thm]{Chú ý}
\newtheorem{dn}[thm]{Định nghĩa}
\newtheorem{vidu}[thm]{Ví dụ}
\newtheorem{bt}{}[section]
% miscellaneous

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\begin{document}
\parskip4pt
\renewcommand{\baselinestretch}{1.1}

\frontmatter

\tableofcontents
\normalsize
\chapter*{Lời nói đầu}
Thử xem thế nào.\\
Let's try it.\\
\chapter*{Các ký hiệu}
\markleft{\sc Các ký hiệu}
\markright{\sc Các ký hiệu}
Ta sẽ dùng các ký hiệu sau \\
We will use these following notations.\\
\mainmatter

\pagenumbering{arabic}

\markleft{\hfill \sc Nguyễn Minh Hà}
\chapter{Hướng của đoạn thẳng}

\markright{\sc Hướng của đoạn thẳng\hfill\ }
\section{Hình thang và hình bình hành}
We define the following figure.\\
\section{Đoạn thẳng}
We define the following arc.\\
\backmatter

\begin{thebibliography}{99}
\end{thebibliography}
\end{document}


So, how can I fix my template to get the correct content with \mathsection, number of section, the name of the section, and the number of page?

• Do you want the symbol \S to appear in the table of contents, in the document and also when using cross-references to a section? I mean, if you cross-reference a section do you want the reference to also show the \S symbol? – Gonzalo Medina Apr 11 '13 at 3:56
• Please see my updated answer. – Gonzalo Medina Apr 11 '13 at 16:59
• @Gonzalo Medina: Thanks, so, what should I add into the template so that the symbol \S appears im the table of content ? – Knumber10 Apr 12 '13 at 3:21
• My code code already puts the symbol in the Table of contents. Don't forget to run the document twice. If the symbol is not appearing for you, let me know. – Gonzalo Medina Apr 12 '13 at 3:54

Since your document class is amsbook and not one of the standard ones, it's better not to use titlesec; the following code contains the necessary redefinitions for the sectional units and will also add the symbol in front of the number in the ToC:

\documentclass[11pt,a4paper]{amsbook}
\usepackage{bbold,amscd,amsmath,amssymb,amsfonts,ifthen,amsthm}
\usepackage[utf8]{vietnam}
\usepackage[all]{xypic}
\usepackage{kpfonts}
%%%%% FOR SEARCHING LABELS AND REFS %%%%%%%%%%%%%%%
\usepackage{color}
\usepackage[color,notref,notcite]{showkeys}
\definecolor{refkey}{rgb}{0,0,0}
\definecolor{labelkey}{rgb}{0,0,1}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\usepackage{newcent}
%\usepackage[unicode]{hyperref}
\usepackage{cmap}

%%%%%MARGIN %%%%%%%%%%%%%%%%%%%
\oddsidemargin 2cm %0.3cm
\evensidemargin 2cm % 3cm
\topmargin2cm
\textwidth12cm %15
\textheight18.5cm %22
\topskip3ex
%% FOR TYPESETTING VIETNAMESE WITH AMSART %%%%%%
\def\firstofone#1{#1}
\let\uppercase\firstofone
\let\MakeUppercase\firstofone
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

%STYLE%%%%%%%%%%%
\def\thepart{\Roman{part}}
\def\thechapter{\arabic{chapter}}
\def\thesection{\arabic{section}}
\def\labelenumi{\roman{enumi})}
%\numberwithin{thm}{section}
\numberwithin{equation}{section}

%THEOREM%%%%%%%%%%%%%%%%
\theoremstyle{plain}
\newtheorem{thm}{Theorem}[section]
\newtheorem{dl}[thm]{Định lý}
\newtheorem{bd}[thm]{Bổ đề}
\newtheorem{hq}[thm]{Hệ quả}
\newtheorem{md}[thm]{Mệnh đề}
\theoremstyle{definition}
\newtheorem{nx}[thm]{Nhận xét}
\newtheorem{chuy}[thm]{Chú ý}
\newtheorem{dn}[thm]{Định nghĩa}
\newtheorem{vidu}[thm]{Ví dụ}
\newtheorem{bt}{}[section]
% miscellaneous

% Chapter and section headings
\makeatletter
\begingroup
\fontsize{\@xivpt}{18}\bfseries\centering
\ifnum\c@secnumdepth>\m@ne
\leavevmode \hskip-\leftskip
\rlap{\vbox to\z@{\vss
\centerline{\normalsize\mdseries
\@xp{\scshape{\chaptername}}\enspace\thechapter}
\vskip 2pc}}\hskip\leftskip\fi
\normalfont\scshape#1\par \endgroup
\vskip\skip@ }
\begingroup
\fontsize{\@xivpt}{18}\normalfont\scshape\centering
#1\par \endgroup
\vskip\skip@ }
\def\@sect#1#2#3#4#5#6[#7]#8{%
\edef\@toclevel{\ifnum#2=\@m 0\else\number#2\fi}%
\ifnum #2>\c@secnumdepth \let\@secnumber\@empty
\else \@xp\let\@xp\@secnumber\csname the#1\endcsname\fi
\ifnum#2=1 \def\@secnumber{\S\thesection}\fi
\ifnum #2>\c@secnumdepth
\let\@svsec\@empty
\else
\refstepcounter{#1}%
\edef\@svsec{\ifnum#2<\@m
\@ifundefined{#1name}{}{%
\ignorespaces\csname #1name\endcsname\space}\fi
\@nx\textup{%
\csname the#1\endcsname.}\enspace
}%
\fi
\@tempskipa #5\relax
\ifdim \@tempskipa>\z@ % then this is not a run-in section heading
\begingroup\ifnum#2=1\relax\noindent\textbf{\S}\fi #6\relax% NEW
\@hangfrom{\hskip #3\relax\@svsec}{\interlinepenalty\@M #8\par}%
\endgroup
\csname #1mark\endcsname{#7}%
\ifnum#2>\@m \else \@tocwrite{#1}{#8}\fi
\else
\def\@svsechd{#6\hskip #3\@svsec
\@ifnotempty{#8}{\ignorespaces#8\unskip
\ifnum#2>\@m \else \@tocwrite{#1}{#8}\fi
}%
\fi
\global\@nobreaktrue
\@xsect{#5}}
\def\section{\@startsection{section}{1}%
\z@{.7\linespacing\@plus\linespacing}{.5\linespacing}%
{\normalfont\bfseries}}
\makeatother
%%%%%%%%%%%%%%%%%%%%%%%%%

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\begin{document}
\parskip4pt
\renewcommand{\baselinestretch}{1.1}

\frontmatter

\tableofcontents
\normalsize
\chapter*{Lời nói đầu}
Thử xem thế nào.\\
Let's try it.\\
\chapter*{Các ký hiệu}
\markleft{\sc Các ký hiệu}
\markright{\sc Các ký hiệu}
Ta sẽ dùng các ký hiệu sau \\
We will use these following notations.\\
\mainmatter

\pagenumbering{arabic}

\markleft{\hfill \sc Nguyễn Minh Hà}
\chapter{Hướng của đoạn thẳng}

\markright{\sc Hướng của đoạn thẳng\hfill\ }
\section{Hình thang và hình bình hành}
We define the following figure.\\
\section{Đoạn thẳng}
We define the following arc.\\
\backmatter

\begin{thebibliography}{99}
\end{thebibliography}
\end{document}
\documentclass[11pt,a4paper]{amsbook}

\begin{document}

\chapter{Test Chapter}
\section{Test Numbered Section}
\section*{Test Unnumbered Section}

\end{document}


I've also changed the answer in the question linked, to not use titlesec.

A final remark: the AMS document classes were designed for submissions to the AMS, thus they have very specific settings that, as you have seen, might be difficult to override.

If you are not bounded to use one of the AMS classes, I would suggest you to switch to another document class; doing so, might be a good trade, since changes in formatting could now be easily done using existing packages (which are incompatible with the AMS classes). As an example, take the following document which produces your formatting (both in the document and in the ToC) with minimal effort and also incorporates some of the stylist settings from amsbook:

\documentclass{book}
\usepackage[compact]{titlesec}
\usepackage[titles]{tocloft}
\usepackage{chngcntr}

\counterwithout{section}{chapter}

\newlength\mylen
\renewcommand\cftchappresnum{\chaptername~}
\renewcommand\cftchapaftersnum{.}
\renewcommand\cftchapfont{\normalfont}
\renewcommand\cftchappagefont{\normalfont}
\settowidth\mylen{\cftchappresnum\cftchapaftersnum} % extra space
\renewcommand\cftsecdotsep{\cftnodots}
\renewcommand\cftsecpresnum{\S}
\renewcommand\cftsecaftersnum{.}

\titleformat{\chapter}[display]
{\normalfont\LARGE\scshape\filcenter}{\chaptertitlename\ \thechapter}{15pt}{}
\titleformat{\section}
{\normalfont\Large\bfseries}{\S\thesection.}{0.5em}{}

\begin{document}

\tableofcontents

\frontmatter
\chapter{Test Chapter}
\chapter{Test Chapter}

\mainmatter
\chapter{Test Chapter}
\section{Test Section}
\section{Test Section}
\chapter{Test Chapter}
\section{Test Section}
\section{Test Section}

\end{document}
`