$k$ sends on $l$ with tag ${\it tg}$ [$s$,$v$.$f$($s$;$v$)], at marker $n$
\\[0ex]$\,\equiv$$_{\mbox{\scriptsize def}}$$\;\;$$\langle$$k$$,\,$$l$$\rangle$ : $\langle$${\it tg}$$,\,$$n$$,\,$($\lambda$$s$,$v$. $f$($s$;$v$).nil)$\rangle$.nil