Существование абсолютно непрерывных функций c заданной последовательностью наилучших рациональных приближений

For a fixed sequence {ап |пі>0 of non-negative real numbers strictly decreasing to zero a absolutely continuous 2n -periodic function f is constructed such that RT n(f) = an, n=0, I, 2, .... where the R'_ (/) are the best approximations of/in the uniform norm by rational trigonometric functions of degree at most n