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D.2.4.5 Crep
Procedure from library grobcov.lib (see grobcov_lib).
- Usage:
- Crep(ideal N,ideal M);
ideal N (null ideal) (not necessarily radical nor
maximal) in Q[a]. (a=parameters, x=variables).
ideal M (hole ideal) (not necessarily containing N)
in Q[a]. To be called in a ring Q[a][x] or a ring Q[a].
But the ideals can contain only the parameters
in Q[a].
- Return:
- The canonical C-representation [P,Q] of the
locally closed set, formed by a pair of radical
ideals with P included in Q, representing the set
V(P) \ V(Q) = V(N) \ V(M)
Example:
| | LIB "grobcov.lib";
short=0;
if(defined(R)){kill R;}
ring R=0,(a,b,c),lp;
ideal p=a*b;
ideal q=a,b-2;
// C-representation of V(p) \ V(q)
Crep(p,q);
==> [1]:
==> _[1]=ab
==> [2]:
==> _[1]=b-2
==> _[2]=a
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