([Equation   7] (δ^((L)))=(∑_(k=1)^k)(Subscript[w, k]^((L+1)))·(δ^((L+1)))·f'((u^(L-1)))
That   is   (δ^((L-1)))=(∑_(k=1)^k)(Subscript[w, k]^((L)))·(δ^((L)))·f'((u^((L-1))))(6))