The Operator Valued Autoregressive Filter Problem and the Suboptimal   Nehari Problem in Two Variables
  Necessary and sufficient conditions are given for the solvability of the operator valued two-variable autoregressive filter problem. In addition, in the two variable suboptimal Nehari problem sufficient conditions are given for when a strictly contractive little Hankel has a strictly contractive symbol. 
J. S. Geronimo H. J. Woerdeman