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Flatness criterion using Fitting ideals
We consider a finitely presented A-module M:
The k-th Fitting ideal is defined as

Fk(M):= ideal generated by the n-k minors of S

Flatness criterion

M is flat of rank r

iff

Fr(M) = A and Fr-1(M) = 0
Flattening Stratification
Application to Singularities

Lille, 08-07-02 http://www.singular.uni-kl.de