Sergei Ovchinnikov is Professor Emeritus of Mathematics at San Francisco State University. His other Universitext books are Measure, Integral, Derivative: a Course on Lebesgue's Theory (2013) and Graphs and Cubes (2011). 

Preface.- 1. Preliminaries.- 2. Metric Spaces.- 3. Special Spaces.- 4. Normed Spaces.- 5. Linear Functionals.- 6. Fundamental Theorems.- 7. Hilbert Spaces.- A. Hilbert Spaces L2(J).- References.- Index.