In this paper, we provide conditions for a nonlinear dynamic model to be the solution of a theoretical setting where agents have a nonlinear looking-Forward behaviour, and where the exogenous effects of both Uncertainty and Levels are allowed to vary through time (according to a multivariate AR-GARCH representation). This so-called FUL model is used to assess the way uncertainty influences investment in Belgium (53-98), a controversal topic in the recent literature devoted to that key economic variable
