1. Wahlquist, H.D., Estabrook, F.B. Prolongation structures of nonlinear evolution equations. Journal of Mathematical Physics, 16: 1–7 (1975)
2. Estabrook, F.B., Wahlquist, H.D. Prolongation structures of nonlinear evolution equations. Journal of Mathematical Physics, 17: 1293–1297 (1976)
3. Zhao, W.Z, Bai, Y.Q., Wu, K. Generalized Inhomogeneous Heisenberg Ferromagnet Model and Generalized Nonlinear Schrödinger Equation. Physics Letters A, 3: 52–64 (2006)
4. Zhai, Y., Albeverio, S., Zhao, W.Z., Wu, K. Prolongation structure of the (2+1)-dimensional integrable Heisenberg ferromagnet model. Journal of A: Mathematical and General, 39: 2117–2126 (2006)
5. Zhang, Z.H., Deng, M., Zhao, W.Z., Wu, K. On the (2+1)-Dimensional Integrable Inhomogeneous Heisenberg Ferromagnet Equation. Journal of the Physical Society of Japan, 75: 104002 (2006)