The stability of each of the theories of separably closed fields is proved, in the manner of Shelah's proof of the corresponding result for differentially closed fields. These are at present the only known stable but not superstable theories of fields. We indicate in § 3 how each of the theories of separably closed fields can be associated with a model complete theory in the language of differential algebra. We assume familiarity with some basic facts about model completeness [4], stability (...) [7], separably closed fields [2] or [3], and (for § 3 only) differential fields [8]. (shrink)

We define a complete theory SHF e of separably closed fields of finite invariant e (= degree of imperfection) which carry an infinite stack of Hasse-derivations. We show that SHF e has quantifier elimination and eliminates imaginaries.