code: def add_clink(self,my_clink):
          
          if self.causalRelations_layer is None:
              self.causalRelations_layer = CcausalRelations()
              self.root.append(self.causalRelations_layer.get_node())
          self.causalRelations_layer.add_clink(my_clink)
docs: Adds a clink to the causalRelations layer
          @type my_clink: L{Cclink}
          @param my_clink: clink object