Initial and final chapters appearing in the table of contents without numbering

Question

I'm editing a document whose preamble starts with

\documentclass [12pt, a4paper]{extbook}

I wish the chapter 'Introduction and its sections' appear in table contents at the beginning of the text before the unnumbered chapter 1.

I also would like a chapter that I call 'Prelude' and its sections' appear in table contents at the beginning of the text before the unnumbered chapter 1.

How can I do this?

Introduction ................................................. .................

             nontechnical introduction .........................

             intrudução technique .................................

             structure of the thesis ....................................

Chapter 1 ................................................ ..................

             Section 1 ..................................

             Section 2 ..................................

             Section 3 ..................................

Chapter 9 ................................................ ................

             Section 1 ..................................

             Section 2 ..................................

             Section 3 ..................................

Prelude ..................................................................

             Other open issues .........................

             New techniques ............................

Answer 1

I think you are looking for the starred versions of the \section, \part etc and a \addcontentsline{toc}{}{}.

For example:

\documentclass[12pt,a4paper]{extbook}

\begin{document}
    \tableofcontents
    \chapter*{Introduction}\addcontentsline{toc}{chapter}{Introduction}
        \section*{nontechnical introduction}\addcontentsline{toc}{section}{nontechnical introduction}
        \section*{intrudução technique}\addcontentsline{toc}{section}{intrudução technique}
        \section*{structure of the thesis}\addcontentsline{toc}{section}{structure of the thesis}

    \chapter{Chapter 1}
        \section{Section 1}
        \section{Section 2}

    \chapter{Chapter 9}
        \section{Section 1}
        \section{Section 2}

    \chapter*{Prelude}\addcontentsline{toc}{chapter}{Prelude}
        \section*{Other open issues}\addcontentsline{toc}{section}{Other open issues}
        \section*{New techniques}\addcontentsline{toc}{section}{New techniques}
\end{document}