  The Calkin algebra is not isomorphic to the corona of the stabilization of
the Cuntz algebra~${\mathcal O}_\infty$, any other Kirchberg algebra, or even
the corona of the stabilization of any unital, ${\mathcal Z}$-stable ${\mathrm
C}^*$-algebra. The proof relies on properties of relative commutants of
separable ${\mathrm C}^*$-subalgebras.
