Approximating classes of functions defined by operators of   differentiation or operators of generalised translation by means of algebraic   polynomials
  In this paper, approximation by means of algebraic polynomials of classes of functions defined by a generalised modulus of smoothness of operators of differentiation of these functions is considered. We give structural characteristics of classes of functions defined by the order of best approximation by algebraic polynomials. 
Nimete Sh. Berisha, Faton M. Berisha
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