Before revision:  The aim of this paperis to show a certain equivalence between these scheduling policiesfor the special case when the multiclass population have identical and exponential service requirements. In fact , we show  the equivalence between two broader classes of policies that generalize the above mentioned four policies.
After revision:  The aim of this paperis to show a certain equivalence between these scheduling policiesfor the special case when the multiclass population have identical and exponential service requirement with parameter \mu , we show the equivalence between two broader classes of policies that generalize the above mentioned four policies.