$\forall$${\it the\_w}$:World, $e$, ${\it e'}$:E. FairFifo $\Rightarrow$ ($e$ $<$loc ${\it e'}$ $\Leftarrow\!\Rightarrow$ (loc($e$) = loc(${\it e'}$) $\in$ Id \& $e$ $<$c ${\it e'}$))