Let Bn := {b0, b1, . . . , bn} (n = 0, 1, . . . , N ; N ∈ N) be the sets of linearly independent functions. We give a simple method of construction the dual functions Dn := { d (n) 0 , d (n) 1 , . . . , d (n) n } (0 ≤ n ≤ N) satisfying the following conditions: spanDn = spanBn and 〈 bi, d (n) j 〉 = δij (0 ≤ i, j ≤ n ≤ N), where δii = 1, δij = 0 for i 6= j, and 〈·, ·〉 is a given inner product. T...