    function _beforeTokenTransfer(
        address _from,
        address _to,
        uint256
    ) internal override {
@>      _checkpoint([_from, _to]);
    }

    function _checkpoint(address[2] memory _accounts) internal nonReentrant {
        //if shutdown, no longer checkpoint in case there are problems
@>      if (isShutdown()) return;

        uint256 supply = _getTotalSupply();
        uint256[2] memory depositedBalance;
        depositedBalance[0] = _getDepositedBalance(_accounts[0]);
        depositedBalance[1] = _getDepositedBalance(_accounts[1]);

        IRewardStaking(convexPool).getReward(address(this), true);

        _claimExtras();

        uint256 rewardCount = rewards.length;
        for (uint256 i = 0; i < rewardCount; i++) {
            _calcRewardIntegral(i, _accounts, depositedBalance, supply, false);
        }
    }    
    function _checkpoint(address[2] memory _accounts) internal nonReentrant {
        //if shutdown, no longer checkpoint in case there are problems
 -      if (isShutdown()) return;

        uint256 supply = _getTotalSupply();
        uint256[2] memory depositedBalance;
        depositedBalance[0] = _getDepositedBalance(_accounts[0]);
        depositedBalance[1] = _getDepositedBalance(_accounts[1]);

        IRewardStaking(convexPool).getReward(address(this), true);

        _claimExtras();

        uint256 rewardCount = rewards.length;
        for (uint256 i = 0; i < rewardCount; i++) {
            _calcRewardIntegral(i, _accounts, depositedBalance, supply, false);
        }
    }    
