  In their proof of the positive energy theorem, Schoen and Yau showed that
every asymptotically flat spacelike hypersurface M of a Lorentzian manifold
which is flat along M can be isometrically imbedded with its given second
fundamental form into Minkowski spacetime as the graph of a function from R^n
to R; in particular, M is diffeomorphic to R^n. In this short note, we give an
alternative proof of this fact. The argument generalises to the asymptotically
hyperbolic case, works in every dimension n, and does not need a spin
structure.
