In one hundred and nine well-packed pages one finds an exposition which is always fresh, proofs which are sophisticated, and a choice of subject matter which is certainly timely. ... Most pages exhibit a zest for play as well as work which is refreshing. - E. R. Lorch (Bull. Amer. Math. Soc.) | Introduction to Hilbert Space and the Theory of Spectral Multiplicity by Paul R. Halmos, Paperback | Indigo Chapters