top-method
If M is a module in a polynomial ring R, then the implementations of
top
and
removeLowestDimension
are based on the following observations:
codim Ext^d(M,R) >= d, for all d (if the module is non-zero)
If P is an associated prime of M of codimension d := codim P > codim M, then codim Ext^d(M,R) = d and the annihilator of Ext^d(M,R) is contained in P
If codim Ext^d(M,R) = d, then there really is an associated prime of codimension d.
If M is R/I, then top(I) = ann Ext^c(R/I,R), where c = codim I
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