 A world, then, is a set of propositions that could be both maximal in this sense and such that all of its members are true. Equivalently put: a set of propositions is a world just in case, possibly, its members are exactly the true propositions that actually  exist.[85]  It follows in particular that the proposition \(\neg \sfE!\sfa\) that Adams doesn’t exist is not true in any world story; for, by strict actualism, since it is a singular proposition about Adams, it couldn’t be true without Adams existing—in which case, of course, it would be false. Very much unlike Prior, however, it does not follow for Adams that his non-existence is not possible, \(\neg\Diamond\neg \sfE!\sfa\).