On approximation of functions by trigonometric polynomials with incomplete spectrum in Lp, 0 < p < 1

Let B be a set of integers with certain arithmetic properties. We obtain estimates of the best approximation of functions in the space L _p , 0 < p <1, by trigonometric polynomials that are constructed by the system {e^ikx}_{k ? mathbbZB} {e^{ikx}}_{kin mathbb{Z}backslash B} . Bibliography: 13 titles.