msg{-}spec{-}loc(${\it snd}$; $i$)
\\[0ex]$\,\equiv$$_{\mbox{\scriptsize def}}$$\;\;$$\forall$$l$:IdLnk. ($l$ $\in$ msg{-}spec{-}links(${\it snd}$) $\in$ IdLnk) $\Rightarrow$ (source($l$) = $i$ $\in$ Id)