Upper estimate of the best accuracy of derivative reconstruction based   on the values of functions of Besov classes with mixed smoothness
  The work provides an upper estimate of the best accuracy for the problem of reconstructing derivatives based on function values at a given number of points for the functions of Besov classes meeting the mixed Hoelder conditions. In some cases this estimate appears to be stronger than the earlier respective estimate obtained by the author in the problem being considered. 
S. N. Kudryavtsev
math.CA