Exact spatial energy identities before expansion of drift commutators.

theorem AVenhance.Infra.Section4.iterateSpatialWord_periodic {f : Homogenization.Vec 2 → ℝ} (hf : ContDiff ℝ (↑⊤) f) (hp : IsZ2Periodic f) (w : List (Fin 2)) : IsZ2Periodic (iterateSpatialWord w f)

Every ordered spatial word of a smooth periodic scalar is periodic.