  For a Hamiltonian system in R^{2n}, its two-system is defined in the phase
space R^{2n} x sp(2n,R). In a sense, it is a combination of the original system
and its system in variations with feedback. We study the Hamiltonian forms of
the two-system and its analogs. In particular, we show a relation between the
Poisson-Lie bracket on the (dual space to) Lie algebra sp(2n,R) and the
canonical bracket.
