?                                                                  // Fill in deepest_child_edge for the parent if not filled in already, or if we beat what's there.                                 // Also maintain parent's second_deepest_child_edge.                                 auto parent_deepest_child_it = deepest_child_edge.find(parent_head);                                 if (parent_deepest_child_it == deepest_child_edge.end()) {                                     // Emplace in the map where we didn't find anything.                                     deepest_child_edge.emplace_hint(parent_deepest_child_it, parent_head, parent_child_edge);                                 } else if(records[find(parent_deepest_child_it->second)].leaf_path_length < child_record.leaf_path_length) {                                     // We are longer than what's there now                                                                          // Demote what's there to second-best                                     parent_record.second_deepest_child_edge = parent_deepest_child_it->second;                                     parent_record.has_second_deepest_child = true;                                                                          // Replace the value we found                                     parent_deepest_child_it->second = parent_child_edge;                                 } else if (!parent_record.has_second_deepest_child) {                                     // There's no second-deepest recorded so we must be it.                                     parent_record.second_deepest_child_edge = parent_child_edge;                                     parent_record.has_second_deepest_child = true;                                 } else if (records[find(parent_record.second_deepest_child_edge)].leaf_path_length < child_record.leaf_path_length) {                                     // We are a new second deepest child.                                     parent_record.second_deepest_child_edge = parent_child_edge;                                 }                                                                 // Now the 