Algebraic properties of the 1+1 dimensional Heisenberg spin field model
  The Estabrook-Wahlquist prolongation method is applied to the (compact and noncompact) continuous isotropic Heisenberg model in 1 + 1 dimensions. Using a special realization (an algebra of the Kac-Moody type) of the arising incomplete prolongation Lie algebra, a whole family of nonlinear field equations containing the original Heisenberg system is generated. 
E. Alfinito, M. Leo, R. A. Leo, M. Palese and G. Soliani