returns an ideal which is contained in the ideal_expression, such that the i-th
generator is a univariate polynomial in the i-th ring variable.
The polynomials have minimal degree w.r.t. this property.
Assume:
The ideal must be zero-dimensional and given as a reduced Groebner basis in
the current ring.
Example:
ring r=0,(x,y,z), dp;
ideal i=y3+x2,x2y+x2,z4-x2-y;
option(redSB); // force computation of reduced basis
i=std(i);
ideal k=finduni(i);
print(k);
==> x4-x2,
==> y4+y3,
==> z12