$\forall$${\it ds}$:$x$:Id fp$\rightarrow$ Type, ${\it da}$:$k$:Knd fp$\rightarrow$ Type, ${\it snd}$:msg{-}spec(${\it ds}$;${\it da}$).
\\[0ex]msg{-}spec{-}links(${\it snd}$) $\in$ IdLnk List