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D.4.7.1 canonMap

Procedure from library homolog.lib (see homolog_lib).

Usage:
canonMap(id); id= ideal/module,

Return:
a list L, the kernel in two different representations and
the cokernel of the canonical map
M ---> Ext^c_R(Ext^c_R(M,R),R) given by presentations
Here M is the R-module (R=basering) given by the presentation
defined by id, i.e. M=R/id resp. M=R^n/id
c is the codimension of M
L[1] is the preimage of the kernel in R resp. R^n
L[2] is a presentation of the kernel
L[3] is a presentation of the cokernel

Example:
 


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