A Bi-Hamiltonian Structure for the Integrable, Discrete Non-Linear   Schrodinger System
  This paper shows that the Ablowitz-Ladik hierarchy of equations (a well-known integrable discretization of the Non-linear Schrodinger system) can be explicitly viewed as a hierarchy of commuting flows which: (a) are Hamiltonian with respect to both a standard, local Poisson operator J and a new non-local, skew, almost Poisson operator K, on the appropriate space; (b) can be recursively generated from a recursion operator R (obtained by composing K and the inverse of J.) In addition, the proof of these facts relies upon two new pivotal resolvent identities which suggest a general method for uncovering bi-Hamiltonian structures for other families of discrete, integrable equations. 
Nicholas M. Ercolani (Dept. of Mathematics, University of Arizona,   Tucson, AZ, USA), Guadalupe I. Lozano (Dept. of Mathema...