  In the paper we discuss Fomenko conjecture on realization of topology of
topology of Liouville foliaions of smooth and real-analytic integrable
Hamiltonian systems by integrable billiards. Vedyushkina-Kharcheva algorithm of
3-atom realization by billiard books is described clearly in the terms of
$f$-graphs. Note, that an arbitrary type of base of Liouville foliation on the
whole isoenergy surface was also realized by V. Vedyushkina and I. Kharcheva
algorithm. In this paper this algorithm is visually applied to realization of a
well-known Zhukovskii integrable system (Euler system with a gyrostat) in a
certain energy zone. It turns out that Liouville foliation is also realized
using this construction, not only the class of its base. Thus, Liouville
equivalence of these billiard and mechanical systems is shown. Then we discuss
V. Kibkalo and V. Vedyushkina result on constructing of a billiard with an
arbitrary numerical invariant. Existence of Fomenko-Zieschang invariant is
proved for some subclass of billiard books without potential. Also, it is
proved that such systems are topologically stable. In the end of the paper we
show that planar billiard system in some potential field can have a
non-degenerate rank 1 4-singularity singularity not satisfying non-splitting
condition.
  Keywords: mathematical billiard, billiard book, integrable Hamiltonian
system, rigid body dynamics, Liouville foliation, Fomenko-Zieschang invariant,
singularity.
