Extending non-standard valuations on function fields to finite extension not implemented

[swewers]

The following code raises a NotimplementedError:

sage: R.<x> = QQ[]
sage: v0 = GaussValuation(R, QQ.valuation(2)).augmentation(x,1)
sage: F.<x> = FunctionField(QQ)
sage: v1 = F.valuation(v0)
sage: v = F.valuation((v1, F.hom([~x]), F.hom([~x])))
sage: S.<y> = F[]
sage: F1.<y> = F.extension(y^2-x^3-1)
sage: v.extension(F1)

The workaround in mclf is to use v.mac_lane_approximants(y^2-x^3-1), which is what an internal implementation would do anyway. So this is not an urgent matter.