“…Figure 1 shows the Fourier space for the trigonometric degree, as well as for the product trigonometric degree, which measures the distance in the ∞-norm, to be used in the next section. The trigonometric degree and similar quantities, originating in the Russian literature, have been studied in many Western publications, some of them by James Lyness [6,16,17,18]; other references are [1,11,10,7,3,2,8,9,5,23].…”