A Comparison Theorem for Eigenfunctions
C. A. Swanson · Proceedings of the American Mathematical Society · 1973
A comparison theorem of Sturm’s type is obtained for eigenfunctions of general linear elliptic partial differential operators of second order on bounded domains of n-dimensional Euclidean space. The proof is almost immediate from an earlier identity of the author. The theorem is shown to be stronger than some recent theorems of Kurt Kreith.