Graded cofinite rings of differential operators

We study subrings of a ring of differential operators such that the extension of associated graded rings is finite. We show that up to an automorphism these subrings correspond exactly to uniformly ramified finite morphisms. This generalizes a theorem of Levasseur-Stafford on the generators of the invariants of a Weyl algebra under a finite group.

Appeared in: Michigan Math. J. 54 (2006) 3-24 Available files:

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Original article (Project Euclid)

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Last updated: April 16, 2006