\documentclass{article}
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\topmargin 0.05truein                % do not modify          %
\oddsidemargin 0.4truein             % do not modify          %
\evensidemargin -.19truein           % do not modify          %
\textheight 8.0truein                % do not modify          %
\textwidth 6.0truein                 % do not modify          %
\headsep 0.5truein                   % do not modify          %
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\pagestyle{myheadings}               % do not modify          %
\def\a{\scriptsize XIII Encuentro Andaluz de Matem\'atica Discreta, 5 al 7 de julio de 2023, Cádiz, España.}                             %
\def\h{\small\underline{\hbox{\a}}}                           %
\markboth{\h}{\h}                    % do not modify          %
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% All necessary packages: Add any other you would need.

\usepackage{graphicx,tikz,color,url}
\usepackage{mathtools}
\usepackage{xspace}
\usepackage[T1]{fontenc}

\usepackage{amsfonts,amsmath,amssymb,cite}
\usepackage{amsmath,amsthm}
\usepackage{enumerate}
\usepackage{latexsym}

\usepackage{amssymb}  %%% uncomment some or all of           %%
\usepackage{amsmath}  %%% these lines in case you            %%
\usepackage{latexsym} %%% want to load the packages          %

%
\newtheorem{theorem}{Theorem}[section]
\newtheorem{definition}[theorem]{Definition}
\newtheorem{lemma}[theorem]{Lemma}
\newtheorem{proposition}[theorem]{Proposition}
\newtheorem{observation}[theorem]{Observation}
\newtheorem{conjecture}[theorem]{Conjecture}
\newtheorem{corollary}[theorem]{Corollary}
\newtheorem{remark}[theorem]{Remark}
\newtheorem{fact}[theorem]{Fact}
\newtheorem{problem}[theorem]{Problem}
\newtheorem{property}[theorem]{Property}


\title{A Small \LaTeX{} Article Template\thanks{Thanks}}
\author{Your Name  \\
	Your Company / University  \\
	\and
	The Other Dude \\
	His Company / University \\
    \and
    The Third Dude \\
	His Company / University \\
	}

\date{\today}
% Hint: \title{what ever}, \author{who care} and \date{when ever} could stand
% before or after the \begin{document} command
% BUT the \maketitle command MUST come AFTER the \begin{document} command!
\begin{document}

\maketitle


\begin{abstract}
Short introduction to subject of the paper \ldots no more than 10 lines. The whole work cannot be longer than 4 pages.
\end{abstract}

\section{Introduction}

Here we write the introduction, and add a Figure if necessary, either in Tikz or as follows. The whole work cannot be longer than 4 pages.

\begin{figure}[h]
  \centering
  %\includegraphics[width=\textwidth]{grafo23}
  \includegraphics[width=8cm]{grafo23}
  \caption{Graph}\label{grafo23}
\end{figure}


\section{Results}

Add the results you have obtained. Long proof might be avoided, and can be included at an Appendix. The whole work cannot be longer than 4 pages.

\begin{theorem}
If $a=b$, then $b=a$.
\end{theorem}

\begin{proof}
It is straightforward.
\end{proof}

\section{Conclusions}\label{conclusions}
There is no longer \LaTeX{} example which was written by \cite{doe}.


\begin{thebibliography}{9}
\bibitem{doe} John Doe,\emph{First and last \LaTeX{} example.}, Journal name 45, (2010) 44-55.
\end{thebibliography}

\end{document}