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Here is one way to get the generators of the Orlik-Solomon ideal:
sage: M = matroids.CompleteGraphic(3)
sage: OS = M.orlik_solomon_algebra(QQ)
sage: E.<x,y,z> = algebras.Exterior(QQ)
sage: d = [[((-1)^i,tuple(list(c)[:i]+list(c)[i+1:])) for i in range(len(c))] for c in M.circuits()]
sage: rels = [E.sum([sgn*E.basis()[idx] for sgn,idx in c]) for c in d]; rels
[x*y - x*z + y*z]
