made stack sort compile

lessons/tris/stack_sort.tex

-\documentclass[a4paper,11pt,dvips]{article}
-\usepackage{epsfig}
+\documentclass[a4paper,11pt]{article}
 \usepackage[T1]{fontenc}
 \usepackage[latin1]{inputenc}
 \usepackage{amsmath}
+\usepackage{graphicx}
 
 \pagestyle{myheadings}
 %\markright{Tri à deux piles}
@@ -86,7 +86,8 @@ tous les
 \begin{center}
 \begin{figure}[ht]
 \begin{center}
-\epsfig{file=figures/stack_sort_expl.eps, width=12cm, height=9cm}
+% \epsfig{file=figures/stack_sort_expl.eps, width=12cm, height=9cm}
+\includegraphics{figures/stack_sort_expl.pdf}
 \end{center}
 \caption{Utilisation des deux piles pour le tri}
 \label{fig1}