Admissibility of a solution to generalized Chaplygin gas

It is known that there is a solution to the Riemann problem for generalized Chaplygin gas model and that it contains the Dirac delta function in some cases. In some cases, usual admissible criteria can not extract a unique weak solution as it was shown in [4]. The aim of this paper is to use a solution to perturbed generalized Chaplygin model by a small constant ?? > 0 and obtain a its unique limit. A weak solution to the unperturbed system that equals that limit is called admissible. The perturbation is made by using the modified model of Chaplygin gas defined in [5].