\documentclass[12pt,oneside]{Thesis}
\usepackage[spanish,mexico]{babel}
\usepackage[sectionbib, square, comma, numbers, sort&compress]{natbib}
\hypersetup{urlcolor=black, colorlinks=true}
\usepackage{amsmath}
\usepackage{mathrsfs}
\usepackage{indentfirst}
\usepackage{enumitem}
\usepackage{url}
\usepackage{float}
\usepackage[colorinlistoftodos, prependcaption, textsize=tiny]{todonotes}
\setlength{\parindent}{0.5cm}
\newcommand{\tr}{\mathrm{tr}}
\newcommand{\diag}{\mathrm{diag}}
\renewcommand{\qedsymbol}{\rule{0.5em}{0.5em}}
\usepackage[spanish]{cleveref}
\usepackage[spanish]{babelbib}
\selectbiblanguage{spanish}
\usepackage{siunitx}
\usepackage{booktabs}
\usepackage{bbm}
\usepackage[many]{tcolorbox}
\usepackage[toc]{appendix}
\newtheorem{observacion}[teorema]{Observaci\'on}
\newtheorem{hipotesis}[teorema]{Hip\'otesis}
\usepackage{xpatch}
\xpatchcmd{\proof}{\itshape}{\normalfont\proofnamefont}{}{}
%%%%%%%%$%%%%%%%%
%Este pequeño bloque permite que el número de la ecuación permanezca del tamaño del resto del texto
%si se decide hacer small el tamaño de la ecuación.
%%%%%%%%%%%%%%%%%
\makeatletter
\def\maketag@@@#1{\hbox{\m@th\normalfont\normalsize#1}}
\makeatother
%%%%%%%%%%%%%%%%
\newcommand{\proofnamefont}{\bfseries}
\begin{document}
\frontmatter
\setstretch{1.5}
\fancyhead{}
\rhead{\thepage}
\lhead{}
\pagestyle{fancy}
\newcommand{\HRule}{\rule{\linewidth}{0.5mm}}
\hypersetup{pdftitle={\titulo}}
\hypersetup{pdfauthor=\autor}
%---------------------------------------------------------------------------
\input{Portada}
\input{Dedicatoria}
\input{Agradecimientos}
%\listoftodos
\input{Contenido}
\mainmatter
\pagestyle{fancy}
\input{Introduccion/Introduccion}
\input{Capitulos/Capitulo1/Capitulo1}
\input{Capitulos/Capitulo2/Capitulo2}
\input{Capitulos/Capitulo3/Capitulo3}
\begin{appendices}
\input{Apendice}
\end{appendices}
%---------------------------------------------------------------------------
% BIBLIOGRAPHY
%---------------------------------------------------------------------------
\label{Bibliography}
\lhead{\emph{Bibliograf\'ia}}
\bibliographystyle{plainnat}
\bibliography{library}
\end{document}