    function _withdraw(
        address operator,
        address src,
        address dst,
        uint256 amount
    ) internal {
        if (!hasPermission(src, operator)) revert Unauthorized();
        // {Comet}
        uint256 srcBalUnderlying = underlyingBalanceOf(src);
        if (srcBalUnderlying < amount) amount = srcBalUnderlying;
        if (amount == 0) revert BadAmount();

        underlyingComet.accrueAccount(address(this));
        underlyingComet.accrueAccount(src);

        uint256 srcBalPre = balanceOf(src);
        CometInterface.UserBasic memory wrappedBasic = underlyingComet.userBasic(address(this));
        int104 wrapperPrePrinc = wrappedBasic.principal;

        // conservative rounding in favor of the wrapper
        IERC20(address(underlyingComet)).safeTransfer(dst, (amount / 10) * 10);

        wrappedBasic = underlyingComet.userBasic(address(this));
        int104 wrapperPostPrinc = wrappedBasic.principal;

        // safe to cast because principal can't go negative, wrapper is not borrowing
        uint256 burnAmt = uint256(uint104(wrapperPrePrinc - wrapperPostPrinc));
        // occasionally comet will withdraw 1-10 wei more than we asked for.
        // this is ok because 9 times out of 10 we are rounding in favor of the wrapper.
        // safe because we have already capped the comet withdraw amount to src underlying bal.
        // untested:
        //      difficult to trigger, depends on comet rules regarding rounding
        if (srcBalPre <= burnAmt) burnAmt = srcBalPre;

        accrueAccountRewards(src);
        _burn(src, safe104(burnAmt));
    }
    function underlyingBalanceOf(address account) public view returns (uint256) {
        uint256 balance = balanceOf(account);
        if (balance == 0) {
            return 0;
        }
        return convertStaticToDynamic(safe104(balance));
    }
    function convertStaticToDynamic(uint104 amount) public view returns (uint256) {
        (uint64 baseSupplyIndex, ) = getUpdatedSupplyIndicies();
        return presentValueSupply(baseSupplyIndex, amount);
    }
    function getUpdatedSupplyIndicies() internal view returns (uint64, uint64) {
        TotalsBasic memory totals = underlyingComet.totalsBasic();
        uint40 timeDelta = uint40(block.timestamp) - totals.lastAccrualTime;
        uint64 baseSupplyIndex_ = totals.baseSupplyIndex;
        uint64 trackingSupplyIndex_ = totals.trackingSupplyIndex;
        if (timeDelta > 0) {
            uint256 baseTrackingSupplySpeed = underlyingComet.baseTrackingSupplySpeed();
            uint256 utilization = underlyingComet.getUtilization();
            uint256 supplyRate = underlyingComet.getSupplyRate(utilization);
            baseSupplyIndex_ += safe64(mulFactor(baseSupplyIndex_, supplyRate * timeDelta));
            trackingSupplyIndex_ += safe64(
                divBaseWei(baseTrackingSupplySpeed * timeDelta, totals.totalSupplyBase)
            );
        }
        return (baseSupplyIndex_, trackingSupplyIndex_);
    }
    function principalValueSupply(uint64 baseSupplyIndex_, uint256 presentValue_)
        internal
        pure
        returns (uint104)
    {
        return safe104((presentValue_ * BASE_INDEX_SCALE) / baseSupplyIndex_);
    }
