msg{-}spec(${\it ds}$; ${\it da}$) $\,\equiv$$_{\mbox{\scriptsize def}}$$\;\;$fpf((:Knd $\times$ IdLnk); ${\it kl}$.(msg{-}item(${\it ds}$; ${\it da}$; (${\it kl}$.1); (${\it kl}$.2)) List))