\left(a_{1}, a_{2}, \ldots, a_{i}, b_{1}, b_{2}, \ldots, b_{j}, c_{1}, c_{2}, \ldots, c_{k}\right) \mapsto \left\{\begin{array}{c} \begin{array}{l} \left(a_{1} + a_{2} + \ldots + a_{i}+ b_{1} + b_{2} + \ldots + b_{j}+ c_{1} + c_{2} + \ldots + c_{k}\right) = \\ \left(a_{1} + a_{2} + \ldots + a_{i} + \left(b_{1} + b_{2} + \ldots + b_{j}\right)+ c_{1} + c_{2} + \ldots + 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..