Comment on "A counterpart of the WKI soliton hierarchy associated with so(3,R)"

Abstract

In the recent paper (Wen-Xiu Ma, Solomon Manukure and Hong-Chan Zheng, arXiv:1405.1089), the authors proposed an integrable hierarchy different from the well-known Wadati-Konno-Ichikawa (WKI) hierarchy. However, using a simple linear change of dependent variables, one can check that their hierarchy is equivalent to the WKI hierarchy. For the same reason, some "new integrable" hierarchies proposed by Wen-Xiu Ma and coworkers in recent e-prints are equivalent to the already known ones.