1. E. Amaldi and E. Fermi, On the absorption and the diffusion of slow neutrons, Phys. Rev. 50 (1936), pp. 899–928.
2. N. I. Akhiezer and I. M. Glazman, Theory of linear operators in Hilbert space (volumes I and II), London and Scottish Academic Press, Edinburgh, 1981.
3. S. Agmon, Spectral properties of Schrödinger operators, in Actes, Congrès intern. Math., vol. 2, pp. 679–683, 1970.
4. S. Agmon, Spectral properties of Schrödinger operators and scattering theory, Ann. Scuola Norm. Sup. Pisa Cl. Sci. (4) 2 (1975), pp. 151–218.
5. S. Agmon, On positivity and decay of solutions of second order elliptic equations on Riemannian manifolds, in Methods of Functional Analysis and Theory of Elliptic Equations, pp. 19–52, Liguori Editore, Naples, 1982.