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Working with a polynomial ring $R$, if I have an ideal generated by a set of polynomials $f_i$ (taking two for concreteness), I can obtain a Groebner basis $g_j$ by the commands

I = R.ideal([f1, f2])
g = I.groebner_basis()

What I want to do is express the Groebner basis in terms of the original basis, i.e. $g_j = \sum_i a_{ij} f_i$. How can I accomplish this in Sage? My understanding is that such an expression is calculated implicitly when the Groebner basis is calculated, so perhaps it is possible to recover it directly from the algorithm.