0$ is active. Also, for any $0 \leq s \leq d_0$, by denoting ${\mbox{\boldmath $X$}}_i = (x_0 \cdots x_{d_0})^T$ and ${\mbox{\boldmath $w$}}_s = (w_0 \cdots w_{d_0})$ for the sake of simplicity, $\vert \varphi(U_s^{(0)}) \vert \leq \vert U_s^{(0)} \vert  =\vert {\mbox{\boldmath $X$}}_i^T {\mbox{\boldmath $w$}}_s \vert  \leq \sum_{t=0}^{d_0} \vert x_t \vert \vert w_t \vert  \leq \alpha \sum_{t=0}^{d_0} (0/d_0) = \alpha$. Hence, according to the assumption of mathematical induction, the first term of the right-hand-side of Eq. (\[eqn0-0\]) is nearly equal to $(0/0)^{H-0}$. In addition, the second term of the right-hand-side of Eq. (\[eqn0-0\]) is nearly equal to 