1. A unique continuation theorem for solutions of elliptic partial differential equations or inequalities of second order;Aronszajn, N.;J. Math. Pures Appl. (9),1957
2. Über Knoten von Eigenfunktionen des Laplace-Beltrami-Operators;Brüning, Jochen;Math. Z.,1978
3. T. Carleman, Sur les systémes linéares aux dérivées partielles du premier ordre á deux variables, C. R. Acad. Sci. Paris Ser. I Math. 197 (1933), 471-474.
4. Finiteness theorems for Riemannian manifolds;Cheeger, Jeff;Amer. J. Math.,1970
5. Nodal sets of eigenfunctions on Riemannian manifolds;Donnelly, Harold;Invent. Math.,1988