\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} {\otimes} a_{2} {\otimes} \ldots {\otimes} a_{i} {\otimes} \left(b_{1} {\otimes} b_{2} {\otimes} \ldots {\otimes} b_{j}\right){\otimes} c_{1} {\otimes} c_{2} {\otimes} \ldots {\otimes} c_{k}\right) \\ = \left(a_{1} {\otimes} a_{2} {\otimes} \ldots {\otimes} a_{i}{\otimes} b_{1} {\otimes} b_{2} {\otimes} \ldots {\otimes} b_{j}{\otimes} c_{1} {\otimes} c_{2} {\otimes} \ldots {\otimes} c_{k}\right) \end{array} \end{array} \textrm{ if } \left(a_{1} \in U_{1}\right) , \left(a_{2} \in U_{2}\right) , \ldots , \left(a_{i} \in U_{i}\right), \left(b_{1} \in V_{1}\right) , \left(b_{2} \in V_{2}\right) , \ldots , \left(b_{j} \in V_{j}\right), \left(c_{1} \in W_{1}\right) , \left(c_{2} \in W_{2}\right) , \ldots , \left(c_{k} \in W_{k}\right)\right..