$\forall$$w$:World, $e$, ${\it e'}$:E.
\\[0ex]FairFifo $\Rightarrow$ (loc($e$) = loc(${\it e'}$) $\in$ Id) $\Rightarrow$ ($e$ $<$ ${\it e'}$ $\Leftarrow\!\Rightarrow$ (time($e$) $<$ time(${\it e'}$)))