Everyone knows that dragons don't exist. But while this simplistic formulation may satisfy the layman,

Everyone knows that dragons don't exist. But while this simplistic
formulation may satisfy the layman, it does not suffice for the
scientific mind. The School of Higher Neantical Nillity is in fact
wholly unconcerned with what ____does exist. Indeed, the banality of
existence has been so amply demonstrated, there is no need for us to
discuss it any further here. The brilliant Cerebron, attacking the
problem analytically, discovered three distinct kinds of dragon: the
mythical, the chimerical, and the purely hypothetical. They were all,
one might say, nonexistent, but each nonexisted in an entirely
different way ...
-- Stanislaw Lem, "Cyberiad"