% Dans le préambule
% -----------------
\usepackage{tikz}
% -----------------

\begin{tikzpicture}[node distance=3cm, bend angle=15]
\tikzstyle{ci}=[circle, draw, inner sep=0pt, minimum width=15pt]
\node[ci] (a){A};
\node[ci] (b)[right of=a] {B};

\draw[fleche] (a) to[bend left]
                  node[above] {$1-x$} (b);
\draw[fleche] (b) to[bend left]
                  node[below] {$1-y$} (a);
\draw[fleche] (a) to[loop left] node[left] {$x$} (a);
\draw[fleche] (b) to[loop right] node[right] {$y$} (b);
\end{tikzpicture}