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% cambio de la apariencia de los capítulos

%\newcommand{\thechapter}{\Roman{chapter}}
\titleformat{\chapter}[display]
 {\bfseries\Huge}
 {\filleft\MakeUppercase{\chaptertitlename} \Huge\thechapter}
 {4ex}
 {\bigrule\vspace{1pt}\titlerule
   \vspace{2ex} %
   \filcenter}
 [\vspace{2ex}%
  \titlerule]

% cambio de la apariencia de las partes

\newcommand{\parttitlename}{\bfseries\Huge Parte}
\titleformat{\part}[display]
{\bfseries\Huge\filcenter}
{\bigrule%
\vspace{1pt}%
\titlerule
\vspace{1pc}%
\underline{\LARGE\MakeUppercase{\parttitlename} \thepart}} {1pc}{}
%{\titlerule
%\vspace{1pc}%
%}
[ \vspace{1pc}%
\titlerule
\vspace{1pt}%
\bigrule]
