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7.7.17.0. dmodoublext
Procedure from library nchomolog.lib (see nchomolog_lib).

Usage:
dmodoublext(M [,i]); M module, i optional int

Compute:
a presentation of Ext^i(Ext^i(M,D),D) for basering D

Return:
left module

Note:
by default, i is set to the integer part of the half of number of variables of D
for holonomic modules over Weyl algebra, the double ext is known to be holonomic left module

Example:
 


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