VDCN, chapter 5 (Specifying systems in Lace), page 518

     A consistency condition applies to names used  in  an
     Ace:  the  Cluster_name  must  be  different for each
     cluster. It  is  valid,  however,  to  use  the  same
     identifier   in   two   or   more  of  the  roles  of
     Cluster_name, System_name, Class_name.