code: def dereference(self):
          
          all = []
          indexes = {}
          for child in self.children:
              child.content(all)
          deplist = DepList()
          for x in all:
              x.qualify()
              midx, deps = x.dependencies()
              item = (x, tuple(deps))
              deplist.add(item)
              indexes[x] = midx
          for x, deps in deplist.sort():
              midx = indexes.get(x)
              if midx is None:
                  continue
              d = deps[midx]
              log.debug('(%s) merging %s <== %s', self.tns[1], Repr(x), Repr(d))
              x.merge(d)
docs: Instruct all children to perform dereferencing.