An extension of integrable equations related to AKNS and WKI spectral problems and their reductions

A novel hierarchy of integrable nonlinear evolution equations related to the combined Ablowitz-Kaup-Newell-Segur (AKNS) and Wadati-Konno-Ichikawa (WKI) spectral problems is proposed, from which the Lax pair for a corresponding negative flow and its infinite many conservation laws are obtained. Furthermore, a reduction of this hierarchy is discussed, by which a generalized sinh-Gordon equation is derived on the basis of its negative flow.