  We explicitly show the fully non-linear equivalence of the $\delta$N and the
covariant formalisms for the superhorizon curvature perturbations, which
enables us to safely evaluate the non-Gaussian quantities of the curvature
perturbation in either formalism. We also discuss isocurvature perturbations in
the covariant formalism and clarify the relation between the fully non-linear
evolution of the curvature covector and that of the curvature perturbation for
multiple interacting fluids.
