$e$ sends $\parallel$ $a$ $\,\equiv$$_{\mbox{\scriptsize def}}$$\;\;$$\forall$${\it e'}$:E. ($\uparrow$isrcv(${\it e'}$)) $\Rightarrow$ (sender(${\it e'}$) = $e$) $\Rightarrow$ val(${\it e'}$):valtype(${\it e'}$)$\parallel$$a$