var [const] unique = Utils.Helpers.listUnique;
class Set {
   fcn init { var [const] set = (vm.arglist.copy() : unique(_)) }
   fcn holds(x) { set.holds(x) }
   fcn union(setB) { self(set.xplode(),setB.set.xplode()) }
   fcn intersection(setB){ sb:=setB.set;
      C:=self(); sc:=C.set;
      foreach x in (set){ if (sb.holds(x)) sc.append(x) }
      C
   }
   fcn diff(setB){ C:=self(); C.set.extend(set);
      setB.set.pump(Void,C.set.remove);
      C
   }
   fcn isSubset(setB){ sb:=setB.set;
      set.pump(Void,'wrap(x){
         if (not sb.holds(x)) return(Void.Stop,False); True
      })
   }
   fcn __opEQ(setB) { ((set.len() == setB.set.len()) and self.isSubset(setB)) }
}