  Let $K$ be a field and $S = K[x_1,\dots,x_n]$ be a polynomial ring over $K$.
We discuss the behaviour of the extremal Betti numbers of the class of
squarefree strongly stable ideals. More precisely, we give a numerical
characterization of the possible extremal Betti numbers (values as well as
positions) of such a class of squarefree monomial ideals.
