B\"acklund loop algebras for compact and non-compact nonlinear spin   models in $(2+1)$ dimensions
  The B\"acklund problem is solved for both the compact and noncompact versions of the Ishimori (2+1)-dimensional nonlinear spin model. In particular, a realization of the arising B\"acklund algebra in the form of an infinite-dimensional loop Lie algebra of the Ka\v{c}--Moody type is provided. 
Marcella Palese (Dept. Math. Univ. Torino, Italy)