标题采用大号粗体字体

Question

我希望标题Fredholm Integral Transforms以大号粗体文本显示。\HUGE字体没有变化。

    \documentclass{book}
    
    \usepackage{geometry}
    \geometry{ paperheight=21cm, paperwidth=21cm, left=8mm, right=8mm,
      top=21mm, bottom=21mm}
    
    \usepackage{type1cm}
    \makeatletter
    \renewcommand\normalsize{%
       \@setfontsize\normalsize{13pt}{13pt}
       \abovedisplayskip 10\p@ \@plus2\p@ \@minus5\p@
       \abovedisplayshortskip \z@ \@plus3\p@
       \belowdisplayshortskip 6\p@ \@plus3\p@ \@minus3\p@
       \belowdisplayskip \abovedisplayskip
       \let\@listi\@listI}
    \makeatother
    
    \begin{document}
    \normalsize
    
    \begin{titlepage}
      \begin{flushleft}
        {\HUGE Fredholm Integral Transforms}
      \end{flushleft}
      \noindent\rule{19cm}{3pt}
    
      \vspace*{\fill}
      \date{\today}
      \begin{flushleft}
       An Author
       \noindent\rule{19cm}{1pt}
      \end{flushleft}
      
    \end{titlepage}
    
    %\maketitle
    \tableofcontents
    
    \chapter{Fourier Transform}
    
    \begin{equation} \label{eqn}
      f(\omega) = \int e^{ - i \omega t } f(t)  dt
    \end{equation}
    
    \end{document}