Some uniqueness theorems on Riemannian manifolds with boundary
Chuan-Chih Hsiung · Illinois Journal of Mathematics · 1960
If Mn iS hypersurfce, then t ech point X(P) of M there is only one unit normal vector e, nd for P ssocited with it we shall simply write P.Let Mn be closed oriented Riemnnin mnifold immersed in Euclidean spce En+m.By normal frame Xen+...e+, on the mnifold M we mean a point X of the mnifold M. nd n ordered set of mutually perpen- diculr unit vectors en+, en+m normal to the manifold M. t the point