Homomorphisms and extensions of modules over certain differential polynomial rings

Abstract

There is a well-known simple hereditary noethcrian domain L3; this is the @-algebra (@ a field of characteristic zero) with two generators x, y subject to the relation xy -yx = 1. A is isomorphic to the ring of formal differential operators with polynomial coefficients and so may be regarded as @]~y][.x], where @[y] is the ring of polynomials over Cp in an indeterminate y, and @[y][x] is the ring of noncommutative polynomials over @[y] in an indeterminatc .T with