code: def installedUniqueRequirements(self, target):
      
  
      myDepends = dependentsOf(self.__class__)
      #XXX optimize?
      for dc in self.store.query(_DependencyConnector,
                                 _DependencyConnector.target==target):
          if dc.installee is self:
              #we're checking all the others not ourself
              continue
          depends = dependentsOf(dc.installee.__class__)
          if self.__class__ in depends:
              raise DependencyError(
                  "%r cannot be uninstalled from %r, "
                  "%r still depends on it" % (self, target, dc.installee))
  
          for cls in myDepends[:]:
              #If one of my dependencies is required by somebody
              #else, leave it alone
              if cls in depends:
                  myDepends.remove(cls)
  
      for dc in self.store.query(_DependencyConnector,
                                 _DependencyConnector.target==target):
          if (dc.installee.__class__ in myDepends
              and not dc.explicitlyInstalled):
              yield dc.installee
docs: Return an iterable of things installed on the target that this item
      requires and are not required by anything else.