  A bounded operator $u$ on $X$ is called rigid when there is an increasing
sequence of positive integers $(n_k)_{k\geq 1}$, such that for every $x$ in $X$
we have $\lim_{k \rightarrow +\infty} u^{n_k} x = x$. For any $r$ in $[0,1]$,
we construct a rigid bounded operator of $l^2$ the spectrum of which is
$\{\lambda \in \mathbb C: r \leq | \lambda | \leq 1\}$. For $0 < r < 1$, it
gives the first examples of rigid bounded invertible operators, such that their
inverse is not rigid.
