  | #### D.4.2.12 nonZeroEntry Procedure from library `algebra.lib` (see algebra_lib). Usage: nonZeroEntry(id); id=object for which the test 'id[i]!=0', i=1,..,N, N=size(id) (resp. ncols(id) for id of type ideal or module) is defined (e.g. ideal, vector, list of polynomials, intvec,...) Return:
               a list, say l, with l[1] an integer, l[2], l[3] integer vectors:
               - l[1] number of non-zero entries of id
               - l[2] intvec of size l[1] with l[2][i]=i if id[i] != 0
                 in case l[1]!=0 (and l[2]=0 if l[1]=0)
               - l[3] intvec with l[3][i]=1 if id[i]!=0 and l[3][i]=0 else
Note: Example:
    LIB "algebra.lib";
    ring r = 0,(a,b,c),dp;
    poly f = a3c+b3+c2+a;
    intvec v = leadexp(f);
    nonZeroEntry(v);
    ==> [1]:
    ==>    2
    ==> [2]:
    ==>    1,3
    ==> [3]:
    ==>    1,0,1
    intvec w;
    list L = 37,0,f,v,w;
    nonZeroEntry(L);
    ==> [1]:
    ==>    3
    ==> [2]:
    ==>    1,3,4
    ==> [3]:
    ==>    1,0,1,1,0

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