“…Later, a lot of research works concentrated on the shock reflection mainly by experiments and computations. It is observed that there are various different and complicated shock patterns depending on many factors, including the shape of the obstacle, the parameters of the incident shock, etc., see Courant-Friedrichs [12], Ben [2], Glimm-Majda [14], and also [4,5,9,10,13,16,26,28] and the references cited therein. Mathematical analysis of shock reflection-diffraction configurations involves several core difficulties in the analysis of nonlinear PDEs, including nonlinear PDEs of mixed hyperbolic-elliptic type, free boundary problem for nonlinear degenerate elliptic PDEs, corner singularities and so on.…”