function _transfer(address _from, address _to, uint256 _tokenId) private {
    ownershipTokenCount[_to]++;
    teamIndexToOwner[_tokenId] = _to;
    if (_from != address(0)) {
      ownershipTokenCount[_from]--;
      delete teamIndexToApproved[_tokenId];
    }
    Transfer(_from, _to, _tokenId);
  }