“…As for system (1.1), the pressure function in [1] is a function of both v and the new variable, λ, making the two systems similar. However, since the adiabatic gas constant, γ, is equal to one in [1], vacuum can never occur for their system as it can for system (1.1). Furthermore, the wave curves in [1] are monotone in λ, resulting in a considerably simpler analysis of the wave interactions compared with the analysis necessary for the model considered here.…”