The Eigenvalue Problem for Ordinary Differential Equations of the Second Order and Heisenberg's Theory of S-Matrices
Kunihiko Kodaira · American Journal of Mathematics · 1949
Kunihiko Kodaira, The Eigenvalue Problem for Ordinary Differential Equations of the Second Order and Heisenberg's Theory of S-Matrices, American Journal of Mathematics, Vol. 71, No. 4 (Oct., 1949), pp. 921-945