“…The related literature is huge and goes back to Henry Poincaré [24] in 1907. For later works, we mention for examples previous works related to CR maps of Webster [29], Faran [8,9], Forstneric [11], D'Angelo [5], Della Sala et al [6], Ebenfelt [7], Huang [15], Kim-Zaitsev [17], Lamel [19], Reiter [25] and the numerous references therein. For works on proper holomorphic maps, we refer the readers to, e.g., Alexander [1], Chan-Mok [4], Mok [21,23], Mok-Ng [22], Xiao-Yuan [31] and the references therein for more information.…”