\documentclass[a4paper, 11pt,
  % use font = times, % garamond, newcm, lmodern, ...
  % use osf,
  use style = plain,
  % use indent = false,
  title in boldface,
  % title in scshape,
  % title in sffamily,
  theorem in new line,
  emphasize theorems,
  theorem numbering = section,
  % number theorems separately,
  simple name,  % for clever referencing
  name in link, % for clever referencing
]{simplivre}
\usepackage{ProjLib}
\usepackage[
    % lang     = {french},
    type     = {CC},
    modifier = {by},
    version  = {4.0},
    hyperxmp = false,
]{doclicense}

\usepackage{blindtext}

%% \UseLanguage{French}

\numberwithin{equation}{section}
\SwitchTheoremNumbering{example,examples,claim}

\begin{document}

\frontmatter

\TitlePage
  {
    % , logo      = { }  % the logo image
    , title     = { \fontspec{SourceSansPro}[WordSpace={1.25,1,1}]
                    \addfontfeature{LetterSpace=2.0}
                    Title of the book\\(demo of the style \textquote{plain})
                  }
    , author    = { Author Name }
    , date      = { \today[only-year-month] }
    % , date      = { \TheDate{2024-01} }
    , info      = {
                    This text is... \blindtext
                  }
    , license   = { \addfontfeature{Numbers=Lining} \medskip\doclicenseThis }
    , license page name = { Info }
  }

\tableofcontents

\mainmatter

\mainmatter

\part{Basic examples}
\parttext{Some introductory text.}

\chapter{Chapter title}

\section{Section title}

\subsection{Subsection title}

Some introductory text.

\begin{definition}[something]
  Define something.
\end{definition}

\begin{theorem}[some result]\label{thm:result}\index{Theorem on some result}
  The statement.
\end{theorem}

\begin{emphasis}
  Clever reference: \cref{thm:result} (only name: \namecref{thm:result}, only number: \labelcref{thm:result}).
\end{emphasis}

An equation:\index{Euler's equation}
\begin{equation}\label{eq:Euler}
  \mathrm{e}^{\mathrm{i}\pi} + 1 = 0.
\end{equation}

\begin{emphasis}
  Reference of equation: \eqref{eq:Euler} or \cref{eq:Euler}.
\end{emphasis}

\SetTheorem{corollary}{shared counter = subsubsection}
\begin{corollary}[of \cref{thm:result}]\label{cor:result}
  Some corollary.
\end{corollary}
\SetTheorem{corollary}{shared counter = subsection}
\begin{proof}
  Some lines of proof.
\end{proof}

\begin{examples}
  \begin{enumerate}
      \item First example.
      \item Second example.
      \item Third example.
  \end{enumerate}
\end{examples}

\begin{example*}[Important example]
  The numbering is switched in the preamble, thus \verb|example*| is the numbered version while \verb|example| is the unnumbered version.
\end{example*}

\begin{proof}[Proof of \cref{thm:result}]
    Some lines of proof.
\end{proof}

\part{Demonstration}

\blinddocument

\backmatter

\printindex

\end{document}