We note that Eq. ( ) is written out explicitly in a form that depends only on x(x 0 , t), constants, and the initial density ρ 0 (x 0 ). The presence of the latter quantity is simply an artifact associated with the coordinate choice C = x 0 . Indeed, the ρ 0 dependence can be easily removed by transforming to a "uniformizing" choice for C, in terms of which The explicit transformation from x 0 to the uniformizing C can be defined as follows: