“…Continuing in the spirit of the approach by Moyal [5], Wigner [6], Husimi [7], et al, according to which quantum mechanics can be formulated in a natural manner in terms of functions on the classical phase space, recently [8] a different approach has been proposed dealing with probability distributions rather than quasi-probabilities of previous approaches. It is to be remarked that this approach differs from the one initiated by Koopman [9], who had shown how the dynamical transformations of classical mechanics considered as measure preserving transformations of the phase space, induce unitary transformations on the Hilbert space of functions which are square integrable with respect to a Liouville measure over the phase space.…”