We obtain a characterization of right semi-arti-
nian rings which have only trivial derivations and prove that a rigid
(i.e. has only the trivial ring endomorphisms) right semi-artinian
ring R is a field or isomorphic to some Z
pn.
Статті IV International Algebraic Conference in Ukraine. In this volume we complete to publish papers presented at the IV International Algebraic Conference in Ukraine, which took place in Lviv (Lemborg) on August 4--9, 2003.