1. On a simple identity for the characteristic values of a differential operator of the second order (Russian);Gelfand;Dokl. Akad. Nauk SSSR,1953
2. A generalization of the trace concept;Halberg;Duke Math. J.,1960
3. On a formula of Gelfand-Levitan (Russian);Dikii;Uspehi Mat. Nauk,1953
4. The sum of differences of eigenvalues of two self-adjoint operators;Gasymov;Soviet Math. Dokl.,1963
5. Some properties of the eigenfunctions of the Laplace operator on Riemannian manifolds;Minakshisundaram;Can. J. Math.,1949