// Contract: Keep3r
// Target function: function burn(uint amount) external
0 ? checkpoints[account][nCheckpoints - 1].votes : 0;
    }

    /**
     * @notice Determine the prior number of votes for an account as of a block number
     * @dev Block number must be a finalized block or else this function will revert to prevent misinformation.
     * @param account The address of the account to check
     * @param blockNumber The block number to get the vote balance at
     * @return The number of votes the account had as of the given block
     */
    function getPriorVotes(address account, uint blockNumber) public view returns (uint) {
        require(blockNumber < block.number, "getPriorVotes:");

        uint32 nCheckpoints = numCheckpoints[account];
        if (nCheckpoints == 0) {
            return 0;
        }

        // First check most recent balance
        if (checkpoints[account][nCheckpoints - 1].fromBlock <= blockNumber) {
            return checkpoints[account][nCheckpoints - 1].votes;
        }

        // Next check implicit zero balance
        if (checkpoints[account][0].fromBlock > blockNumber) {
            return 0;
        }

        uint32 lower = 0;
        uint32 upper = nCheckpoints - 1;
        while (upper > lower) {
            uint32 center = upper - (upper - lower) / 2; // ceil, avoiding overflow
            Checkpoint memory cp = checkpoints[account][center];
            if (cp.fromBlock == blockNumber) {
                return cp.votes;
            } else if (cp.fromBlock < blockNumber) {
                lower = center;
            } else {
                upper = center - 1;
            }
        }
        return checkpoints[account][lower].votes;
    }

    function _delegate(address delegator, address delegatee) internal {
        address currentDelegate = delegates[delegator];
        uint delegatorBalance = votes[delegator].add(bonds[delegator][address(this)]);
        delegates[delegator] = delegatee;

        emit DelegateChanged(delegator, currentDelegate, delegatee);

        _moveDelegates(currentDelegate, delegatee, delegatorBalance);
    }

    function _moveDelegates(address srcRep, address dstRep, uint amount) internal {
        if (srcRep != dstRep && amount > 0) {
            if (srcRep != address(0)) {
                uint32 srcRepNum = numCheckpoints[srcRep];
                uint srcRepOld = srcRepNum > 0 ? checkpoints[srcRep][srcRepNum - 1].votes : 0;
                uint srcRepNew = srcRepOld.sub(amount, "_moveVotes: underflows");
                _writeCheckpoint(srcRep, srcRepNum, srcRepOld, srcRepNew);
            }

            if (dstRep != address(0)) {
                uint32 dstRepNum = numCheckpoints[dstRep];
                uint dstRepOld = dstRepNum > 0 ? checkpoints[dstRep][dstRepNum - 1].votes : 0;
                uint dstRepNew = dstRepOld.add(amount);
                _writeCheckpoint(dstRep, dstRepNum, dstRepOld, dstRepNew);
            }
        }
    }

    function _writeCheckpoint(address delegatee, uint32 nCheckpoints, uint oldVotes, uint newVotes) internal {
      uint32 blockNumber = safe32(block.number, "_writeCheckpoint: 32 bits");

      if (nCheckpoints > 0 && checkpoints[delegatee][nCheckpoints - 1].fromBlock == blockNumber) {
          checkpoints[delegatee][nCheckpoints - 1].votes = newVotes;
      } else {
          checkpoints[delegatee][nCheckpoints] = Checkpoint(blockNumber, newVotes);
          numCheckpoints[delegatee] = nCheckpoints + 1;
      }

      emit DelegateVotesChanged(delegatee, oldVotes, newVotes);
    }

    function safe32(uint n, string memory errorMessage) internal pure returns (uint32) {
        require(n < 2**32, errorMessage);
        return uint32(n);
    }

    /// @notice The standard EIP-20 transfer event
    event Transfer(address indexed from, address indexed to, uint amount);

    /// @notice The standard EIP-20 approval event
    event Approval(address indexed owner, address indexed spender, uint amount);

    /// @notice Submit a job
    event SubmitJob(address indexed job, address indexed provider, uint block, uint credit);

    /// @notice Apply credit to a job
    event ApplyCredit(address indexed job, address indexed provider, uint block, uint credit);

    /// @notice Remove credit for a job
    event RemoveJob(address indexed job, address indexed provider, uint block, uint credit);

    /// @notice Unbond credit for a job
    event UnbondJob(address indexed job, address indexed provider, uint block, uint credit);

    /// @notice Added a Job
    event JobAdded(address indexed job, uint block, address governance);

    /// @notice Removed a job
    event JobRemoved(address indexed job, uint block, address governance);

    /// @notice Worked a job
    event KeeperWorked(address indexed credit, address indexed job, address indexed keeper, uint block);

    /// @notice Keeper bonding
    event KeeperBonding(address indexed keeper, uint block, uint active, uint bond);

    /// @notice Keeper bonded
    event KeeperBonded(address indexed keeper, uint block, uint activated, uint bond);

    /// @notice Keeper unbonding
    event KeeperUnbonding(address indexed keeper, uint block, uint deactive, uint bond);

    /// @notice Keeper unbound
    event KeeperUnbound(address indexed keeper, uint block, uint deactivated, uint bond);

    /// @notice Keeper slashed
    event KeeperSlashed(address indexed keeper, address indexed slasher, uint block, uint slash);

    /// @notice Keeper disputed
    event KeeperDispute(address indexed keeper, uint block);

    /// @notice Keeper resolved
    event KeeperResolved(address indexed keeper, uint block);

    event AddCredit(address indexed credit, address indexed job, address indexed creditor, uint block, uint amount);

    /// @notice 1 day to bond to become a keeper
    uint constant public BOND = 3 days;
    /// @notice 14 days to unbond to remove funds from being a keeper
    uint constant public UNBOND = 14 days;
    /// @notice 7 days maximum downtime before being slashed
    uint constant public DOWNTIME = 7 days;
    /// @notice 3 days till liquidity can be bound
    uint constant public LIQUIDITYBOND = 3 days;
    
    /// @notice direct liquidity fee 0.3%
    uint constant public FEE = 30;
    /// @notice 5% of funds slashed for downtime
    uint constant public DOWNTIMESLASH = 500;
    uint constant public BASE = 10000;

    /// @notice address used for ETH transfers
    address constant public ETH = address(0xE);

    /// @notice tracks all current bondings (time)
    mapping(address => mapping(address => uint)) public bondings;
    /// @notice tracks all current unbondings (time)
    mapping(address => mapping(address => uint)) public unbondings;
    /// @notice allows for partial unbonding
    mapping(address => mapping(address => uint)) public partialUnbonding;
    /// @notice tracks all current pending bonds (amount)
    mapping(address => mapping(address => uint)) public pendingbonds;
    /// @notice tracks how much a keeper has bonded
    mapping(address => mapping(address => uint)) public bonds;
    /// @notice tracks underlying votes (that don't have bond)
    mapping(address => uint) public votes;

    /// @notice total bonded (totalSupply for bonds)
    uint public totalBonded = 0;
    /// @notice tracks when a keeper was first registered
    mapping(address => uint) public firstSeen;

    /// @notice tracks if a keeper has a pending dispute
    mapping(address => bool) public disputes;

    /// @notice tracks last job performed for a keeper
    mapping(address => uint) public lastJob;
    /// @notice tracks the total job executions for a keeper
    mapping(address => uint) public workCompleted;
    /// @notice list of all jobs registered for the keeper system
    mapping(address => bool) public jobs;
    /// @notice the current credit available for a job
    mapping(address => mapping(address => uint)) public credits;
    /// @notice the balances for the liquidity providers
    mapping(address => mapping(address => mapping(address => uint))) public liquidityProvided;
    /// @notice liquidity unbonding days
    mapping(address => mapping(address => mapping(address => uint))) public liquidityUnbonding;
    /// @notice liquidity unbonding amounts
    mapping(address => mapping(address => mapping(address => uint))) public liquidityAmountsUnbonding;
    /// @notice job proposal delay
    mapping(address => uint) public jobProposalDelay;
    /// @notice liquidity apply date
    mapping(address => mapping(address => mapping(address => uint))) public liquidityApplied;
    /// @notice liquidity amount to apply
    mapping(address => mapping(address => mapping(address => uint))) public liquidityAmount;

    /// @notice list of all current keepers
    mapping(address => bool) public keepers;
    /// @notice blacklist of keepers not allowed to participate
    mapping(address => bool) public blacklist;

    /// @notice traversable array of keepers to make external management easier
    address[] public keeperList;
    /// @notice traversable array of jobs to make external management easier
    address[] public jobList;

    /// @notice governance address for the governance contract
    address public governance;
    address public pendingGovernance;

    /// @notice the liquidity token supplied by users paying for jobs
    mapping(address => bool) public liquidityAccepted;

    address[] public liquidityPairs;

    uint internal _gasUsed;

    constructor() public {
        // Set governance for this token
        governance = msg.sender;
    }

    /**
     * @notice Add ETH credit to a job to be paid out for work
     * @param job the job being credited
     */
    function addCreditETH(address job) external payable {
        require(jobs[job], "addCreditETH: !job");
        uint _fee = msg.value.mul(FEE).div(BASE);
        credits[job][ETH] = credits[job][ETH].add(msg.value.sub(_fee));
        payable(governance).transfer(_fee);

        emit AddCredit(ETH, job, msg.sender, block.number, msg.value);
    }

    /**
     * @notice Add credit to a job to be paid out for work
     * @param credit the credit being assigned to the job
     * @param job the job being credited
     * @param amount the amount of credit being added to the job
     */
    function addCredit(address credit, address job, uint amount) external nonReentrant {
        require(jobs[job], "addCreditETH: !job");
        uint _before = IERC20(credit).balanceOf(address(this));
        IERC20(credit).safeTransferFrom(msg.sender, address(this), amount);
        uint _received = IERC20(credit).balanceOf(address(this)).sub(_before);
        uint _fee = _received.mul(FEE).div(BASE);
        credits[job][credit] = credits[job][credit].add(_received.sub(_fee));
        IERC20(credit).safeTransfer(governance, _fee);
        
        emit AddCredit(credit, job, msg.sender, block.number, _received);
    }

    /**
     * @notice Add non transferable votes for governance
     * @param voter to add the votes to
     * @param amount of votes to add
     */
    function addVotes(address voter, uint amount) external {
        require(msg.sender == governance, "addVotes: !gov");
        votes[voter] = votes[voter].add(amount);
        _moveDelegates(address(0), delegates[voter], amount);
    }

    /**
     * @notice Remove non transferable votes for governance
     * @param voter to subtract the votes
     * @param amount of votes to remove
     */
    function removeVotes(address voter, uint amount) external {
        require(msg.sender == governance, "addVotes: !gov");
        votes[voter] = votes[voter].sub(amount);
        _moveDelegates(delegates[voter], address(0), amount);
    }

    /**
     * @notice Add credit to a job to be paid out for work
     * @param job the job being credited
     * @param amount the amount of credit being added to the job
     */
    function addKPRCredit(address job, uint amount) external {
        require(msg.sender == governance, "addKPRCredit: !gov");
        require(jobs[job], "addKPRCredit: !job");
        credits[job][address(this)] = credits[job][address(this)].add(amount);

        emit AddCredit(address(this), job, msg.sender, block.number, amount);
    }

    /**
     * @notice Approve a liquidity pair for being accepted in future
     * @param liquidity the liquidity no longer accepted
     */
    function approveLiquidity(address liquidity) external {
        require(msg.sender == governance, "approveLiquidity: !gov");
        require(!liquidityAccepted[liquidity], "approveLiquidity: !pair");
        liquidityAccepted[liquidity] = true;
        liquidityPairs.push(liquidity);
    }

    /**
     * @notice Revoke a liquidity pair from being accepted in future
     * @param liquidity the liquidity no longer accepted
     */
    function revokeLiquidity(address liquidity) external {
        require(msg.sender == governance, "revokeLiquidity: !gov");
        liquidityAccepted[liquidity] = false;
    }

    /**
     * @notice Displays all accepted liquidity pairs
     */
    function pairs() external view returns (address[] memory) {
        return liquidityPairs;
    }

    /**
     * @notice Allows liquidity providers to submit jobs
     * @param liquidity the liquidity being added
     * @param job the job to assign credit to
     * @param amount the amount of liquidity tokens to use
     */
    function addLiquidityToJob(address liquidity, address job, uint amount) external nonReentrant {
        require(liquidityAccepted[liquidity], "addLiquidityToJob: !pair");
        IERC20(liquidity).safeTransferFrom(msg.sender, address(this), amount);
        liquidityProvided[msg.sender][liquidity][job] = liquidityProvided[msg.sender][liquidity][job].add(amount);

        liquidityApplied[msg.sender][liquidity][job] = now.add(LIQUIDITYBOND);
        liquidityAmount[msg.sender][liquidity][job] = liquidityAmount[msg.sender][liquidity][job].add(amount);

        if (!jobs[job] && jobProposalDelay[job] < now) {
            IGovernance(governance).proposeJob(job);
            jobProposalDelay[job] = now.add(UNBOND);
        }
        emit SubmitJob(job, msg.sender, block.number, amount);
    }

    /**
     * @notice Applies the credit provided in addLiquidityToJob to the job
     * @param provider the liquidity provider
     * @param liquidity the pair being added as liquidity
     * @param job the job that is receiving the credit
     */
    function applyCreditToJob(address provider, address liquidity, address job) external {
        require(liquidityAccepted[liquidity], "addLiquidityToJob: !pair");
        require(liquidityApplied[provider][liquidity][job] != 0, "credit: no bond");
        require(liquidityApplied[provider][liquidity][job] < now, "credit: bonding");
        uint _liquidity = balances[address(liquidity)];
        uint _credit = _liquidity.mul(liquidityAmount[provider][liquidity][job]).div(IERC20(liquidity).totalSupply());
        _mint(address(this), _credit);
        credits[job][address(this)] = credits[job][address(this)].add(_credit);
        liquidityAmount[provider][liquidity][job] = 0;

        emit ApplyCredit(job, provider, block.number, _credit);
    }

    /**
     * @notice Unbond liquidity for a job
     * @param liquidity the pair being unbound
     * @param job the job being unbound from
     * @param amount the amount of liquidity being removed
     */
    function unbondLiquidityFromJob(address liquidity, address job, uint amount) external {
        require(liquidityAmount[msg.sender][liquidity][job] == 0, "credit: pending credit");
        liquidityUnbonding[msg.sender][liquidity][job] = now.add(UNBOND);
        liquidityAmountsUnbonding[msg.sender][liquidity][job] = liquidityAmountsUnbonding[msg.sender][liquidity][job].add(amount);
        require(liquidityAmountsUnbonding[msg.sender][liquidity][job] <= liquidityProvided[msg.sender][liquidity][job], "unbondLiquidityFromJob: insufficient funds");

        uint _liquidity = balances[address(liquidity)];
        uint _credit = _liquidity.mul(amount).div(IERC20(liquidity).totalSupply());
        if (_credit > credits[job][address(this)]) {
            _burn(address(this), credits[job][address(this)]);
            credits[job][address(this)] = 0;
        } else {
            _burn(address(this), _credit);
            credits[job][address(this)] = credits[job][address(this)].sub(_credit);
        }

        emit UnbondJob(job, msg.sender, block.number, amount);
    }

    /**
     * @notice Allows liquidity providers to remove liquidity
     * @param liquidity the pair being unbound
     * @param job the job being unbound from
     */
    function removeLiquidityFromJob(address liquidity, address job) external {
        require(liquidityUnbonding[msg.sender][liquidity][job] != 0, "removeJob: unbond");
        require(liquidityUnbonding[msg.sender][liquidity][job] < now, "removeJob: unbonding");
        uint _amount = liquidityAmountsUnbonding[msg.sender][liquidity][job];
        liquidityProvided[msg.sender][liquidity][job] = liquidityProvided[msg.sender][liquidity][job].sub(_amount);
        liquidityAmountsUnbonding[msg.sender][liquidity][job] = 0;
        IERC20(liquidity).safeTransfer(msg.sender, _amount);

        emit RemoveJob(job, msg.sender, block.number, _amount);
    }

    /**
     * @notice Allows governance to mint new tokens to treasury
     * @param amount the amount of tokens to mint to treasury
     */
    function mint(uint amount) external {
        require(msg.sender == governance, "mint: !gov");
        _mint(governance, amount);
    }