list<uint32_t> HeaderTable::referenceSet() const {
  list<uint32_t> external;
  for (auto& i : refset_) {
    external.push_back(toExternal(i));
  }
  // seems like the compiler will avoid the copy here
  return external;
}
list<uint32_t> HeaderTable::referenceSet() const {
  list<uint32_t> external;
  for (auto& i : refset_) {
    external.push_back(toExternal(i));
  }
   
  return external;
}