  In the paper there is studied an optimal saving model in which the
interest-rate risk for saving is a fuzzy number. The total utility of
consumption is defined by using a concept of possibilistic expected utility. A
notion of possibilistic precautionary saving is introduced as a measure of the
variation of optimal saving level when moving from a sure saving model to a
possibilistic risk model. A first result establishes a necessary and sufficient
condition that the presence of a possibilistic interest-rate risk generates an
extra-saving. This result can be seen as a possibilistic version of a
Rothschilld and Stiglitz theorem on a probabilistic model of saving. A second
result of the paper studies the variation of the optimal saving level when
moving from a probabilistic model (the interest-rate risk is a random variable)
to a possibilistic model (the interest-rate risk is a fuzzy number).
