Strong discontinuities in 2-submodels of class $E$ of gas dynamic equations

We consider evolutionary invariant submodels with two independent variables of equations of gas dynamics. We discuss the question of the structure of strong discontinuities of the solutions of the corresponding systems of differential equations. These systems have multiple characteristics, though this does not interfere with the analysis of the nature of the strong discontinuities. We study the behavior of the derivatives of the solutions on shock waves. We solve the (local) problem of the interaction of shock waves and weak discontinuities.