Note that any two suitable labelling coordinates must be related to via a bijective function (i.e., monotonic, in the one-dimensional case). In addition, we stress that the labelling coordinate (which could also be termed the "Lagrangian coordinate") is necessarily timeindependent along a given trajectory: C(x(x 0 , t)) = C(x(x 0 , 0)) ∀t. Finally, for each trajectory in the ensemble, we have