Abstract
We introduce the concept of interior ideal and the concept of fuzzy
interior ideal in hypersemigroups and we prove, among others, that in
regular also in intra-regular hypersemigroups the interior ideals and the
fuzzy interior ideals coincide. We also prove that an hypergroupoid H is
simple if and only if every fuzzy ideal of H is a constant function; and
that an hypersemigroup H is simple if and only if every fuzzy interior
ideal of H is a constant function, equivalently if, for every element a of
H, we have H = H * {a} * H.