1. B. M. Levitan, Almost Periodic Functions, Gostekhizdat, Moscow (1953).
2. M.I. Kadetz, ?Integration of almost periodic functions with values in a Banach space,? Funktsional Analiz i Ego Prilozhenia,3, No. 3 (1969).
3. R. Doss, ?On bounded functions with almost periodic differences,? Proc. Amer. Math. Soc.,12, 488?489 (1961).
4. B. R. Boles, ?Generalization of two theorems of M. I. Kadetz on the indefinite integral of an abstract almost periodic function,? Matem. Zametki,9, No. 3 (1971).
5. M. G. Lyubarskii, ?The indefinite integral of an almost periodic function of Levitan,? Theory of Functions, Functional Analysis and Its Applications, No. 16, Izd-vo KhGU (1972).