Soliton equations related to the affine Kac-Moody algebra D^(1)_4
  We have derived the hierarchy of soliton equations associated with the untwisted affine Kac-Moody algebra D^(1)_4 by calculating the corresponding recursion operators. The Hamiltonian formulation of the equations from the hierarchy is also considered. As an example we have explicitly presented the first non-trivial member of the hierarchy, which is an one-parameter family of mKdV equations. We have also considered the spectral properties of the Lax operator and introduced a minimal set of scattering data. 
Vladimir S. Gerdjikov, Dimitar M. Mladenov, Aleksander A. Stefanov,   Stanislav K. Varbev
nlin.SI math-ph math.MP