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## Microlocal structure

The ring of microdifferential operators with constant coefficients

is a discrete valuation ring and is a free -module of rank . For , is bijective and hence is a -automorphism of mapping the trivial -structure to that of . Hence, is a free -module of rank .

In particular, , resp. , is a free -module of rank for , resp. . Hence, is a -dimensional vector space over the quotient field . Since and , is a free -module of rank .

Christoph Lossen
2001-03-21