  The (extended) AGM postulates for belief revision seem to deal with the
revision of a given theory K by an arbitrary formula, but not to constrain the
revisions of two different theories by the same formula. A new postulate is
proposed and compared with other similar postulates that have been proposed in
the literature. The AGM revisions that satisfy this new postulate stand in
one-to-one correspondence with the rational, consistency-preserving relations.
This correspondence is described explicitly. Two viewpoints on iterative
revisions are distinguished and discussed.
