$\forall$${\it es}$:ES, $L$:(Id List). fischer($L$) $\Rightarrow$ ($\forall$$e_{1}$, $e_{2}$:E. Try($e_{1}$) $\Rightarrow$ Try($e_{2}$) $\Rightarrow$ Dec($e_{1}$ $<$f $e_{2}$))