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Thanks for the answer. Actually my \cuatex newcommmand is defined as:

\newcommand{\cuatex}[3]
{\begin{center}
\setlength{\unitlength}{2.54cm}
\begin{picture}(#1,#2)
\put(0,0){\special{eps:quadrado.eps x=#1 in y=#2 in}}
\put(0,0){\framebox(#1,#2){\begin{minipage}{12.5cm}#3\end{minipage}}}
\end ...

What is wrong with the following code?:

\documentclass[11pt]{book}
\usepackage[utf8]{inputenc}
\usepackage{amsmath, amsthm, amssymb, enumerate}

\begin{document}

\newtheorem{defi}{Definición}[section]

\newcommand{\cuatex}[3]
{\begin{center}
\setlength{\unitlength}{2.54cm}
\begin{picture}(#1,#2 ...