$\forall$${\it es}$:ES, ${\it Cmd}$:Type, ${\it Sys}$:AbsInterface(chain\_sys(${\it Cmd}$)).
\\[0ex]input{-}dcdr\{i:l\}(${\it es}$;${\it Cmd}$;${\it Sys}$) $\in$ $e$:E$\rightarrow$Dec(($\uparrow$($e$ $\in_{b}$ ${\it Sys}$)) c$\wedge$ ($\uparrow$csinput?(${\it Sys}$($e$))))