Halmos, Paul R. Introduction to Hilbert space and the theory of spectral multiplicity. - 2d ed. - New York Chelsea Pub. Co. [c1957] - 114 p. LCCN: 57012834 /L/r84 Subjects--Topical Terms: Spectral theory (Mathematics) LC Class. No.: QA691 / .H34 1957 Dewey Class. No.: 513.8