  Representation of classical dynamics by unitary transformations has been used
to develop unified description of hybrid classical-quantum systems with
particular type of interaction, and to formulate abstract systems interpolating
between classical and quantum ones. We solved the problem of unitary
description of two interpolating systems with general potential interaction.
The general solution is used to show that with arbitrary potential interaction
between the two interpolating systems the evolution of the so called
unobservable variables is decoupled from that of the observable ones if and
only if the interpolation parameters in the two interpolating systems are
equal.
