theorem instMaterialEntityAtToParent
theorem instMaterialEntityAtToParent: ∀ (x t : Type) [MaterialEntity.At x t], IndependentContinuant.At x t
theorem instMaterialEntityAtToParent
theorem instMaterialEntityAtToParent: ∀ (x t : Type) [MaterialEntity.At x t], IndependentContinuant.At x t