1. Measure Theory
2. G. H. Hardy, J. E. Littlewood, and G. Pólya, Inequalities, Cambridge, 1934, p. 75.
3. Some theorems on subseries;Hill, J. D.;Bull. Amer. Math. Soc.,1942
4. E. W. Hobson, The theory of functions of a real variable, vol. 1, 3d ed., Cambridge, 1926, pp. 607-608.
5. Subseries of a convergent series;Pollard, Harry;Bull. Amer. Math. Soc.,1943