Problems and Theorems in Analysis I: Series. Integral Calculus. Theory of Functions (Grundlehren der mathematischen Wissenschaften)

From the reviews: "The work is one of the real classics of this century; it has had much influence on teaching, on research in several branches of hard analysis, particularly complex function theory, and it has been an essential indispensable source book for those seriously interested in mathematical problems." Bulletin of the American Mathematical Society