Towards an effective version of a theorem of Stafford

A classical theorem of Stafford says: every left ideal of partial different ial operators with rational or even polynomial coefficients inn variables c an be generated by two elements. The highly involved proof of this theorem is reorganized and completed for rational coefficients in order to yield a procedure which guarantees the computability in finitely many steps. Conseq uences for an eventual normal form for matrices of such operators are discu ssed. (C) 2001 Academic Press.