Further theorems on Fourier coefficients. Integration of fractional order 9.1. Remarks on the theorems of Hausdorff-Young and F. Riesz. 9.2. M. Riesz'a convexity theorems. 9.3. Proof of F. Riesz's theorem. 9.4. Theorems of Paley. 9.5. Theorems of Hardy and Littlewood. 9.6. Banach's theorems on lacunary coefficients. 9.7. Wiener's theorem on functions of bounded variation. 9.8. Integrals of fractional order. 9.9. Miscellaneous theorems and examples.