$e$ $<$c ${\it e'}$ $\,\equiv$$_{\mbox{\scriptsize def}}$$\;\;$$e$ $\lambda$$e$,${\it e'}$. $e$ $<$loc ${\it e'}$ $\vee$ (($\uparrow$isrcv(kind(${\it e'}$))) c$\wedge$ ($e$ = sender(${\it e'}$)))\^{}+ ${\it e'}$