$\forall$$l$:IdLnk, ${\it tg}$:Id, $L$:Top, $l_{1}$:IdLnk, $t_{1}$:Id, $L_{1}$:Top.
\\[0ex]$\neg$$\langle$$l$$,\,$${\it tg}$$\rangle$ $=$ $\langle$$l_{1}$$,\,$$t_{1}$$\rangle$ $\Rightarrow$ (only $L$ sends on ($l$ with ${\it tg}$) $\Vert\!+$ only $L_{1}$ sends on ($l_{1}$ with $t_{1}$))