$$ x \cdot y = \frac{1}{2 \cdot 2 !} \left( (x + y)^2 - (x - y)^2 \right) $$ $$ \begin{eqnarray} x \cdot y \cdot z &=& \frac{1}{2^2 \cdot 3 !} ((x + y + z)^3 - (x + y - z)^3 \nonumber \\ &-& (x - y + z)^3 + (x - y - z)^3 ), \end{eqnarray} $$ $$ \begin{eqnarray} x \cdot y \cdot z \cdot w &=& \frac{1}{2^3 \cdot 4 !} ( (x + y + z + w)^4 \nonumber \\ &-& (x + y + z - w)^4 - (x + y - z + w)^4 \nonumber \\ &+& (x + y - z - w)^4 - (x - y + z + w)^4 \nonumber \\ &+& (x - y + z - w)^4 + (x - y - z + w)^4 \nonumber \\ &-& (x - y - z - w)^4 ). \end{eqnarray} $$ The identity that rewrites a product of $n$ variables $( n \ge 2$, $n \in \boldsymbol{Z_+})$ as additions of $n$ th power functions is as given below: $$ \begin{eqnarray} & &x_0 \cdots x_1 \cdot x_{n-1} = \frac{1}{2^{n - 1} \cdot n !} \cdot \sum_{j = 0}^{2^{ n - 1} -1} ( - 1 )^{\sum_{m = 1}^{n - 1} \sigma_m(j)} \times ( x_0 + (-1)^{\sigma_1(j)} x_1 + \cdots + (- 1)^{\sigma_{n - 1}(j)} x_{n - 1})^n, \\ & &\sigma_m(j) = r(\left\lfloor \frac{j}{2^{m - 1}}\right\rfloor, 2), m (\ge 1), j (\ge 0) \in \boldsymbol{Z_+}, \; \left\lfloor x \right\rfloor = \max \{ n \in \boldsymbol{Z_+} ; n \le x, x \in \boldsymbol{R} \} \end{eqnarray} $$ where $r(\alpha, \beta)$, $\alpha, \beta (\ge 1) \in \boldsymbol{Z_+}$ means the remainder of the division of $\alpha$ by $\beta$ such that $r(\alpha, \beta)$ $=$ $\alpha - \beta \left\lfloor \frac{\alpha}{\beta}\right\rfloor$