LetNn+1be a complete Riemannian manifold with metrich;i, Levi-Civita connectionrand the usual exponential mapping exp :TN!N.Consider a hypersurfaceMnofNn+1. Givenp2Mnand a xed unitaryvector0that is normal toMnatp, we can parametrize a neighborhood ofMncontainingpand contained in a normal ball ofNn+1as(1.1)'(x) = expp(x+(x)0);where the vectorxvaries in a neighborhoodWof zero inTpMand:W!Rsatises(0) = 0. Observe thatis unique.