“…In a number of papers (see, for example, [2,3]), Temlyakov found the orders of the approximation TMr(F)v of classes of periodic functions of several variables by bilinear forms for d = l -d in F (u, v). These are the classes W vq,a , SW;,a , HVq, and YH~ of periodic functions that are defined by restrictions on the corresponding partial derivatives or prelimit differences.…”