\left\{\begin{array}{c} \begin{array}{l} \left(a_{1} \cdot a_{2} \cdot \ldots \cdot a_{i}\cdot b_{1} \cdot b_{2} \cdot \ldots \cdot b_{j}\cdot c_{1} \cdot c_{2} \cdot \ldots \cdot c_{k}\right) = \\ \left(a_{1} \cdot a_{2} \cdot \ldots \cdot a_{i} \cdot \left(b_{1} \cdot b_{2} \cdot \ldots \cdot b_{j}\right)\cdot c_{1} \cdot c_{2} \cdot \ldots \cdot c_{k}\right) \end{array} \end{array} \textrm{ if } \left(a_{1} \in \mathbb{C}\right) , \left(a_{2} \in \mathbb{C}\right) , \ldots , \left(a_{i} \in \mathbb{C}\right), \left(b_{1} \in \mathbb{C}\right) , \left(b_{2} \in \mathbb{C}\right) , \ldots , \left(b_{j} \in \mathbb{C}\right), \left(c_{1} \in \mathbb{C}\right) , \left(c_{2} \in \mathbb{C}\right) , \ldots , \left(c_{k} \in \mathbb{C}\right)\right..