function internal_update_add_user_to_group(uint256 _group_id, address _user, bytes32 _document)
           internal
           returns (bool _success)
  {
    if (system.groups_by_id[_group_id].members_by_address[_user].active == false && system.group_ids_by_address[_user] == 0 && system.groups_by_id[_group_id].role_id != 0) {

      system.groups_by_id[_group_id].members_by_address[_user].active = true;
      system.group_ids_by_address[_user] = _group_id;
      system.groups_collection.append(bytes32(_group_id), _user);
      system.groups_by_id[_group_id].members_by_address[_user].document = _document;
      _success = true;
    } else {
      _success = false;
    }
  }