which is a 6-fold integral. While f is associated with a number of particles, the phase space is for one-particle (not all of them, which is usually the case with deterministic many-body systems), since only one r and p is in question. It is not part of the analysis to use r 1, p 1 for particle 1, r 2, p 2 for particle 2, etc. up to r N, p N for particle N.