Actual smooth representatives of the closed divergence-free space have pointwise lifted divergence zero.
theorem
EulerClassicalDivergence.divergenceFree_classical_divergence_zero
(period : ℝ)
[Fact (0 < period)]
(κ : ℝ)
(m : EulerLiftedGradientSpace.Vector3)
(u : ↥(EulerLiftedGradientSpace.LiftL2 period))
(hu : u ∈ EulerLiftedGradientSpace.divergenceFreeSpace period κ m)
(g : EulerLiftedGradientSpace.LiftDomain period → EulerLiftedGradientSpace.Vector3)
(hrep : ↑↑u =ᵐ[EulerLiftedGradientSpace.liftMeasure period] g)
(hg :
∀ (x : EulerLiftedGradientSpace.LiftDomain period), ContDiff ℝ (↑⊤) (EulerMetricTransport.localFieldLift period g x))
(x : EulerLiftedGradientSpace.LiftDomain period)
:
∑ i : Fin 3,
(EulerTransportDerivatives.fieldDerivative period (EulerMetricTransport.coordinateDirection κ m i) g x).ofLp i = 0
A genuine smooth representative of a weakly lifted-divergence-free L² field has zero pointwise lifted divergence.