2-SIDED IDEALS IN RINGS OF DIFFERENTIAL-OPERATORS AND ETALE HOMOMORPHISMS

Let A be a commutative Noetherian and reduced ring. If A has an etale covering B such that all the irreducible components of B are geometric unibranches, we will construct an invariant ideal gamma(A) of A which has the following properties: If A is an algebra over some ring k, th en gamma(A) is an essential left D(A)-submodule of A, and if all the i rreducible components of B have rings of differential operators that a re simple, then gamma(A) is the minimal essential left D(A)-submodule of A, and D(A, gamma(A)) is the minimal essential two-sided ideal of D (A). (C) 1995 Academic Press, Inc.