For f = P(u)/Q(u) in lowest terms, W(λ, f) = span(1, u, ū, f, f/(s + λu)) is visible to the four-dimensional extensions exactly when a degree bound holds

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For f = P(u)/Q(u) in lowest terms, W(λ, f) = span(1, u, ū, f, f/(s + λu)) is visible to the four-dimensional extensions exactly when a degree bound holds · Prove2Me