theorem instFiatSurfaceAtToParent
theorem instFiatSurfaceAtToParent: ∀ (x t : Type) [FiatSurface.At x t], ContinuantFiatBoundary.At x t
theorem instFiatSurfaceAtToParent
theorem instFiatSurfaceAtToParent: ∀ (x t : Type) [FiatSurface.At x t], ContinuantFiatBoundary.At x t