  It is shown, using a track-level simulation, that the use of the $D_s^- \to
K^{*0}K^-$ decay channel for $D_s^-$ reconstruction, in additioon with the
previously studied $D_s^- \to \phi \pi^-$ mode, enables two fold gain in the
ATLAS $B_s^0$-mixing signal statistics through $B_s^0 \to D_s^-a_1$
$B_s^0$-decay channel. A new modification of the amplitude fit method is
suggested for the $x_s$ determination. Some general aspects of the
$B_s^0$-mixing phenomenon is illustrated by pictures of Casimir Malevich,
Maurits Cornelis Escher and Salvador Dali.
