“…Over the last twenty years, several extensions of important geometric concepts, such as controlled invariance, have been proposed for 2-D latent variable models such as the Fornasini-Marchesini and Roesser state-space models, [5], [6], [12], [13]. While definitions of controlled invariance and output-nulling subspaces are not difficult to establish for FM-I, FM-II or Kurek models, a definition for conditioned invariant subspaces is less natural, since duality cannot be exploited as in the 1-D case.…”