  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.
