pragma solidity ^0.4.18;

contract DelegateERC20 {
  function delegateTotalSupply() public view returns (uint256);
  function delegateBalanceOf(address who) public view returns (uint256);
  function delegateTransfer(address to, uint256 value, address origSender) public returns (bool);
  function delegateAllowance(address owner, address spender) public view returns (uint256);
  function delegateTransferFrom(address from, address to, uint256 value, address origSender) public returns (bool);
  function delegateApprove(address spender, uint256 value, address origSender) public returns (bool);
  function delegateIncreaseApproval(address spender, uint addedValue, address origSender) public returns (bool);
  function delegateDecreaseApproval(address spender, uint subtractedValue, address origSender) public returns (bool);
}

library SafeMath {

  /**
  * @dev Multiplies two numbers, throws on overflow.
  */
  function mul(uint256 a, uint256 b) internal pure returns (uint256) {
    if (a == 0) {
      return 0;
    }
    uint256 c = a * b;
    assert(c / a == b);
    return c;
  }

  /**
  * @dev Integer division of two numbers, truncating the quotient.
  */
  function div(uint256 a, uint256 b) internal pure returns (uint256) {
    // assert(b > 0); // Solidity automatically throws when dividing by 0
    uint256 c = a / b;
    // assert(a == b * c + a % b); // There is no case in which this doesn't hold
    return c;
  }

  /**
  * @dev Substracts two numbers, throws on overflow (i.e. if subtrahend is greater than minuend).
  */
  function sub(uint256 a, uint256 b) internal pure returns (uint256) {
    assert(b <= a);
    return a - b;
  }

  /**
  * @dev Adds two numbers, throws on overflow.
  */
  function add(uint256 a, uint256 b) internal pure returns (uint256) {
    uint256 c = a + b;
    assert(c >= a);
    return c;
  }
}

contract Ownable {
  address public owner;


  event OwnershipTransferred(address indexed previousOwner, address indexed newOwner);


  /**
   * @dev The Ownable constructor sets the original `owner` of the contract to the sender
   * account.
   */
  function Ownable() public {
    owner = msg.sender;
  }

  /**
   * @dev Throws if called by any account other than the owner.
   */
  modifier onlyOwner() {
    require(msg.sender == owner);
    _;
  }

  /**
   * @dev Allows the current owner to transfer control of the contract to a newOwner.
   * @param newOwner The address to transfer ownership to.
   */
  function transferOwnership(address newOwner) public onlyOwner {
    require(newOwner != address(0));
    OwnershipTransferred(owner, newOwner);
    owner = newOwner;
  }

}

contract Pausable is Ownable {
  event Pause();
  event Unpause();

  bool public paused = false;


  /**
   * @dev Modifier to make a function callable only when the contract is not paused.
   */
  modifier whenNotPaused() {
    require(!paused);
    _;
  }

  /**
   * @dev Modifier to make a function callable only when the contract is paused.
   */
  modifier whenPaused() {
    require(paused);
    _;
  }

  /**
   * @dev called by the owner to pause, triggers stopped state
   */
  function pause() onlyOwner whenNotPaused public {
    paused = true;
    Pause();
  }

  /**
   * @dev called by the owner to unpause, returns to normal state
   */
  function unpause() onlyOwner whenPaused public {
    paused = false;
    Unpause();
  }
}

contract CanReclaimToken is Ownable {
  using SafeERC20 for ERC20Basic;

  /**
   * @dev Reclaim all ERC20Basic compatible tokens
   * @param token ERC20Basic The address of the token contract
   */
  function reclaimToken(ERC20Basic token) external onlyOwner {
    uint256 balance = token.balanceOf(this);
    token.safeTransfer(owner, balance);
  }

}

contract Claimable is Ownable {
  address public pendingOwner;

  /**
   * @dev Modifier throws if called by any account other than the pendingOwner.
   */
  modifier onlyPendingOwner() {
    require(msg.sender == pendingOwner);
    _;
  }

  /**
   * @dev Allows the current owner to set the pendingOwner address.
   * @param newOwner The address to transfer ownership to.
   */
  function transferOwnership(address newOwner) onlyOwner public {
    pendingOwner = newOwner;
  }

  /**
   * @dev Allows the pendingOwner address to finalize the transfer.
   */
  function claimOwnership() onlyPendingOwner public {
    OwnershipTransferred(owner, pendingOwner);
    owner = pendingOwner;
    pendingOwner = address(0);
  }
}

contract AddressList is Claimable {
    string public name;
    mapping (address => bool) public onList;

    function AddressList(string _name, bool nullValue) public {
        name = _name;
        onList[0x0] = nullValue;
    }
    event ChangeWhiteList(address indexed to, bool onList);

    // Set whether _to is on the list or not. Whether 0x0 is on the list
    // or not cannot be set here - it is set once and for all by the constructor.
    function changeList(address _to, bool _onList) onlyOwner public {
        require(_to != 0x0);
        if (onList[_to] != _onList) {
            onList[_to] = _onList;
            ChangeWhiteList(_to, _onList);
        }
    }
}

contract HasNoContracts is Ownable {

  /**
   * @dev Reclaim ownership of Ownable contracts
   * @param contractAddr The address of the Ownable to be reclaimed.
   */
  function reclaimContract(address contractAddr) external onlyOwner {
    Ownable contractInst = Ownable(contractAddr);
    contractInst.transferOwnership(owner);
  }
}

contract HasNoEther is Ownable {

  /**
  * @dev Constructor that rejects incoming Ether
  * @dev The `payable` flag is added so we can access `msg.value` without compiler warning. If we
  * leave out payable, then Solidity will allow inheriting contracts to implement a payable
  * constructor. By doing it this way we prevent a payable constructor from working. Alternatively
  * we could use assembly to access msg.value.
  */
  function HasNoEther() public payable {
    require(msg.value == 0);
  }

  /**
   * @dev Disallows direct send by settings a default function without the `payable` flag.
   */
  function() external {
  }

  /**
   * @dev Transfer all Ether held by the contract to the owner.
   */
  function reclaimEther() external onlyOwner {
    assert(owner.send(this.balance));
  }
}

contract HasNoTokens is CanReclaimToken {

 /**
  * @dev Reject all ERC223 compatible tokens
  * @param from_ address The address that is transferring the tokens
  * @param value_ uint256 the amount of the specified token
  * @param data_ Bytes The data passed from the caller.
  */
  function tokenFallback(address from_, uint256 value_, bytes data_) external {
    from_;
    value_;
    data_;
    revert();
  }

}

contract NoOwner is HasNoEther, HasNoTokens, HasNoContracts {
}

contract AllowanceSheet is Claimable {
    using SafeMath for uint256;

    mapping (address => mapping (address => uint256)) public allowanceOf;

    function addAllowance(address tokenHolder, address spender, uint256 value) public onlyOwner {
        allowanceOf[tokenHolder][spender] = allowanceOf[tokenHolder][spender].add(value);
    }

    function subAllowance(address tokenHolder, address spender, uint256 value) public onlyOwner {
        allowanceOf[tokenHolder][spender] = allowanceOf[tokenHolder][spender].sub(value);
    }

    function setAllowance(address tokenHolder, address spender, uint256 value) public onlyOwner {
        allowanceOf[tokenHolder][spender] = value;
    }
}

contract BalanceSheet is Claimable {
    using SafeMath for uint256;

    mapping (address => uint256) public balanceOf;

    function addBalance(address addr, uint256 value) public onlyOwner {
        balanceOf[addr] = balanceOf[addr].add(value);
    }

    function subBalance(address addr, uint256 value) public onlyOwner {
        balanceOf[addr] = balanceOf[addr].sub(value);
    }

    function setBalance(address addr, uint256 value) public onlyOwner {
        balanceOf[addr] = value;
    }
}

contract ERC20Basic {
  function totalSupply() public view returns (uint256);
  function balanceOf(address who) public view returns (uint256);
  function transfer(address to, uint256 value) public returns (bool);
  event Transfer(address indexed from, address indexed to, uint256 value);
}

contract BasicToken is ERC20Basic, Claimable {
  using SafeMath for uint256;

  BalanceSheet balances;

  uint256 totalSupply_;

  function setBalanceSheet(address sheet) external onlyOwner {
    balances = BalanceSheet(sheet);
    balances.claimOwnership();
  }

  /**
  * @dev total number of tokens in existence
  */
  function totalSupply() public view returns (uint256) {
    return totalSupply_;
  }

  /**
  * @dev transfer token for a specified address
  * @param _to The address to transfer to.
  * @param _value The amount to be transferred.
  */
  function transfer(address _to, uint256 _value) public returns (bool) {
    transferAllArgsNoAllowance(msg.sender, _to, _value);
    return true;
  }

  function transferAllArgsNoAllowance(address _from, address _to, uint256 _value) internal {
    require(_to != address(0));
    require(_from != address(0));
    require(_value <= balances.balanceOf(_from));

    // SafeMath.sub will throw if there is not enough balance.
    balances.subBalance(_from, _value);
    balances.addBalance(_to, _value);
    Transfer(_from, _to, _value);
  }

  /**
  * @dev Gets the balance of the specified address.
  * @param _owner The address to query the the balance of.
  * @return An uint256 representing the amount owned by the passed address.
  */
  function balanceOf(address _owner) public view returns (uint256 balance) {
    return balances.balanceOf(_owner);
  }
}

contract BurnableToken is BasicToken {

  event Burn(address indexed burner, uint256 value);

  /**
   * @dev Burns a specific amount of tokens.
   * @param _value The amount of token to be burned.
   */
  function burn(uint256 _value) public {
    require(_value <= balances.balanceOf(msg.sender));
    // no need to require value <= totalSupply, since that would imply the
    // sender's balance is greater than the totalSupply, which *should* be an assertion failure

    address burner = msg.sender;
    balances.subBalance(burner, _value);
    totalSupply_ = totalSupply_.sub(_value);
    Burn(burner, _value);
    Transfer(burner, address(0), _value);
  }
}

contract ERC20 is ERC20Basic {
  function allowance(address owner, address spender) public view returns (uint256);
  function transferFrom(address from, address to, uint256 value) public returns (bool);
  function approve(address spender, uint256 value) public returns (bool);
  event Approval(address indexed owner, address indexed spender, uint256 value);
}

library SafeERC20 {
  function safeTransfer(ERC20Basic token, address to, uint256 value) internal {
    assert(token.transfer(to, value));
  }

  function safeTransferFrom(ERC20 token, address from, address to, uint256 value) internal {
    assert(token.transferFrom(from, to, value));
  }

  function safeApprove(ERC20 token, address spender, uint256 value) internal {
    assert(token.approve(spender, value));
  }
}

contract StandardToken is ERC20, BasicToken {

  AllowanceSheet allowances;

  function setAllowanceSheet(address sheet) external onlyOwner {
    allowances = AllowanceSheet(sheet);
    allowances.claimOwnership();
  }

  /**
   * @dev Transfer tokens from one address to another
   * @param _from address The address which you want to send tokens from
   * @param _to address The address which you want to transfer to
   * @param _value uint256 the amount of tokens to be transferred
   */
  function transferFrom(address _from, address _to, uint256 _value) public returns (bool) {
    transferAllArgsYesAllowance(_from, _to, _value, msg.sender);
    return true;
  }

  function transferAllArgsYesAllowance(address _from, address _to, uint256 _value, address spender) internal {
    require(_value <= allowances.allowanceOf(_from, spender));

    allowances.subAllowance(_from, spender, _value);
    transferAllArgsNoAllowance(_from, _to, _value);
  }

  /**
   * @dev Approve the passed address to spend the specified amount of tokens on behalf of msg.sender.
   *
   * Beware that changing an allowance with this method brings the risk that someone may use both the old
   * and the new allowance by unfortunate transaction ordering. One possible solution to mitigate this
   * race condition is to first reduce the spender's allowance to 0 and set the desired value afterwards:
   * https://github.com/ethereum/EIPs/issues/20#issuecomment-263524729
   * @param _spender The address which will spend the funds.
   * @param _value The amount of tokens to be spent.
   */
  function approve(address _spender, uint256 _value) public returns (bool) {
    approveAllArgs(_spender, _value, msg.sender);
    return true;
  }

  function approveAllArgs(address _spender, uint256 _value, address _tokenHolder) internal {
    allowances.setAllowance(_tokenHolder, _spender, _value);
    Approval(_tokenHolder, _spender, _value);
  }

  /**
   * @dev Function to check the amount of tokens that an owner allowed to a spender.
   * @param _owner address The address which owns the funds.
   * @param _spender address The address which will spend the funds.
   * @return A uint256 specifying the amount of tokens still available for the spender.
   */
  function allowance(address _owner, address _spender) public view returns (uint256) {
    return allowances.allowanceOf(_owner, _spender);
  }

  /**
   * @dev Increase the amount of tokens that an owner allowed to a spender.
   *
   * approve should be called when allowed[_spender] == 0. To increment
   * allowed value is better to use this function to avoid 2 calls (and wait until
   * the first transaction is mined)
   * From MonolithDAO Token.sol
   * @param _spender The address which will spend the funds.
   * @param _addedValue The amount of tokens to increase the allowance by.
   */
  function increaseApproval(address _spender, uint _addedValue) public returns (bool) {
    increaseApprovalAllArgs(_spender, _addedValue, msg.sender);
    return true;
  }

  function increaseApprovalAllArgs(address _spender, uint _addedValue, address tokenHolder) internal {
    allowances.addAllowance(tokenHolder, _spender, _addedValue);
    Approval(tokenHolder, _spender, allowances.allowanceOf(tokenHolder, _spender));
  }

  /**
   * @dev Decrease the amount of tokens that an owner allowed to a spender.
   *
   * approve should be called when allowed[_spender] == 0. To decrement
   * allowed value is better to use this function to avoid 2 calls (and wait until
   * the first transaction is mined)
   * From MonolithDAO Token.sol
   * @param _spender The address which will spend the funds.
   * @param _subtractedValue The amount of tokens to decrease the allowance by.
   */
  function decreaseApproval(address _spender, uint _subtractedValue) public returns (bool) {
    decreaseApprovalAllArgs(_spender, _subtractedValue, msg.sender);
    return true;
  }

  function decreaseApprovalAllArgs(address _spender, uint _subtractedValue, address tokenHolder) internal {
    uint oldValue = allowances.allowanceOf(tokenHolder, _spender);
    if (_subtractedValue > oldValue) {
      allowances.setAllowance(tokenHolder, _spender, 0);
    } else {
      allowances.subAllowance(tokenHolder, _spender, _subtractedValue);
    }
    Approval(tokenHolder, _spender, allowances.allowanceOf(tokenHolder, _spender));
  }

}

contract CanDelegate is StandardToken {
    // If this contract needs to be upgraded, the new contract will be stored
    // in 'delegate' and any ERC20 calls to this contract will be delegated to that one.
    DelegateERC20 public delegate;

    event DelegatedTo(address indexed newContract);

    // Can undelegate by passing in newContract = address(0)
    function delegateToNewContract(DelegateERC20 newContract) public onlyOwner {
        delegate = newContract;
        DelegatedTo(delegate);
    }

    // If a delegate has been designated, all ERC20 calls are forwarded to it
    function transfer(address to, uint256 value) public returns (bool) {
        if (delegate == address(0)) {
            return super.transfer(to, value);
        } else {
            return delegate.delegateTransfer(to, value, msg.sender);
        }
    }

    function transferFrom(address from, address to, uint256 value) public returns (bool) {
        if (delegate == address(0)) {
            return super.transferFrom(from, to, value);
        } else {
            return delegate.delegateTransferFrom(from, to, value, msg.sender);
        }
    }

    function balanceOf(address who) public view returns (uint256) {
        if (delegate == address(0)) {
            return super.balanceOf(who);
        } else {
            return delegate.delegateBalanceOf(who);
        }
    }

    function approve(address spender, uint256 value) public returns (bool) {
        if (delegate == address(0)) {
            return super.approve(spender, value);
        } else {
            return delegate.delegateApprove(spender, value, msg.sender);
        }
    }

    function allowance(address _owner, address spender) public view returns (uint256) {
        if (delegate == address(0)) {
            return super.allowance(_owner, spender);
        } else {
            return delegate.delegateAllowance(_owner, spender);
        }
    }

    function totalSupply() public view returns (uint256) {
        if (delegate == address(0)) {
            return super.totalSupply();
        } else {
            return delegate.delegateTotalSupply();
        }
    }

    function increaseApproval(address spender, uint addedValue) public returns (bool) {
        if (delegate == address(0)) {
            return super.increaseApproval(spender, addedValue);
        } else {
            return delegate.delegateIncreaseApproval(spender, addedValue, msg.sender);
        }
    }

    function decreaseApproval(address spender, uint subtractedValue) public returns (bool) {
        if (delegate == address(0)) {
            return super.decreaseApproval(spender, subtractedValue);
        } else {
            return delegate.delegateDecreaseApproval(spender, subtractedValue, msg.sender);
        }
    }
}

contract StandardDelegate is StandardToken, DelegateERC20 {
    address public delegatedFrom;

    modifier onlySender(address source) {
        require(msg.sender == source);
        _;
    }

    function setDelegatedFrom(address addr) onlyOwner public {
        delegatedFrom = addr;
    }

    // All delegate ERC20 functions are forwarded to corresponding normal functions
    function delegateTotalSupply() public view returns (uint256) {
        return totalSupply();
    }

    function delegateBalanceOf(address who) public view returns (uint256) {
        return balanceOf(who);
    }

    function delegateTransfer(address to, uint256 value, address origSender) onlySender(delegatedFrom) public returns (bool) {
        transferAllArgsNoAllowance(origSender, to, value);
        return true;
    }

    function delegateAllowance(address owner, address spender) public view returns (uint256) {
        return allowance(owner, spender);
    }

    function delegateTransferFrom(address from, address to, uint256 value, address origSender) onlySender(delegatedFrom) public returns (bool) {
        transferAllArgsYesAllowance(from, to, value, origSender);
        return true;
    }

    function delegateApprove(address spender, uint256 value, address origSender) onlySender(delegatedFrom) public returns (bool) {
        approveAllArgs(spender, value, origSender);
        return true;
    }

    function delegateIncreaseApproval(address spender, uint addedValue, address origSender) onlySender(delegatedFrom) public returns (bool) {
        increaseApprovalAllArgs(spender, addedValue, origSender);
        return true;
    }

    function delegateDecreaseApproval(address spender, uint subtractedValue, address origSender) onlySender(delegatedFrom) public returns (bool) {
        decreaseApprovalAllArgs(spender, subtractedValue, origSender);
        return true;
    }
}

contract PausableToken is StandardToken, Pausable {

  function transfer(address _to, uint256 _value) public whenNotPaused returns (bool) {
    return super.transfer(_to, _value);
  }

  function transferFrom(address _from, address _to, uint256 _value) public whenNotPaused returns (bool) {
    return super.transferFrom(_from, _to, _value);
  }

  function approve(address _spender, uint256 _value) public whenNotPaused returns (bool) {
    return super.approve(_spender, _value);
  }

  function increaseApproval(address _spender, uint _addedValue) public whenNotPaused returns (bool success) {
    return super.increaseApproval(_spender, _addedValue);
  }

  function decreaseApproval(address _spender, uint _subtractedValue) public whenNotPaused returns (bool success) {
    return super.decreaseApproval(_spender, _subtractedValue);
  }
}

contract TrueUSD is StandardDelegate, PausableToken, BurnableToken, NoOwner, CanDelegate {
    string public name = "TrueUSD";
    string public symbol = "TUSD";
    uint8 public constant decimals = 18;

    AddressList public canReceiveMintWhiteList;
    AddressList public canBurnWhiteList;
    AddressList public blackList;
    AddressList public noFeesList;
    uint256 public burnMin = 10000 * 10**uint256(decimals);
    uint256 public burnMax = 20000000 * 10**uint256(decimals);

    uint80 public transferFeeNumerator = 7;
    uint80 public transferFeeDenominator = 10000;
    uint80 public mintFeeNumerator = 0;
    uint80 public mintFeeDenominator = 10000;
    uint256 public mintFeeFlat = 0;
    uint80 public burnFeeNumerator = 0;
    uint80 public burnFeeDenominator = 10000;
    uint256 public burnFeeFlat = 0;
    address public staker;

    event ChangeBurnBoundsEvent(uint256 newMin, uint256 newMax);
    event Mint(address indexed to, uint256 amount);
    event WipedAccount(address indexed account, uint256 balance);

    function TrueUSD() public {
        totalSupply_ = 0;
        staker = msg.sender;
    }

    function setLists(AddressList _canReceiveMintWhiteList, AddressList _canBurnWhiteList, AddressList _blackList, AddressList _noFeesList) onlyOwner public {
        canReceiveMintWhiteList = _canReceiveMintWhiteList;
        canBurnWhiteList = _canBurnWhiteList;
        blackList = _blackList;
        noFeesList = _noFeesList;
    }

    function changeName(string _name, string _symbol) onlyOwner public {
        name = _name;
        symbol = _symbol;
    }

    //Burning functions as withdrawing money from the system. The platform will keep track of who burns coins,
    //and will send them back the equivalent amount of money (rounded down to the nearest cent).
    function burn(uint256 _value) public {
        require(canBurnWhiteList.onList(msg.sender));
        require(_value >= burnMin);
        require(_value <= burnMax);
        uint256 fee = payStakingFee(msg.sender, _value, burnFeeNumerator, burnFeeDenominator, burnFeeFlat, 0x0);
        uint256 remaining = _value.sub(fee);
        super.burn(remaining);
    }

    //Create _amount new tokens and transfer them to _to.
    //Based on code by OpenZeppelin: https://github.com/OpenZeppelin/zeppelin-solidity/blob/master/contracts/token/MintableToken.sol
    function mint(address _to, uint256 _amount) onlyOwner public {
        require(canReceiveMintWhiteList.onList(_to));
        totalSupply_ = totalSupply_.add(_amount);
        balances.addBalance(_to, _amount);
        Mint(_to, _amount);
        Transfer(address(0), _to, _amount);
        payStakingFee(_to, _amount, mintFeeNumerator, mintFeeDenominator, mintFeeFlat, 0x0);
    }

    //Change the minimum and maximum amount that can be burned at once. Burning
    //may be disabled by setting both to 0 (this will not be done under normal
    //operation, but we can't add checks to disallow it without losing a lot of
    //flexibility since burning could also be as good as disabled
    //by setting the minimum extremely high, and we don't want to lock
    //in any particular cap for the minimum)
    function changeBurnBounds(uint newMin, uint newMax) onlyOwner public {
        require(newMin <= newMax);
        burnMin = newMin;
        burnMax = newMax;
        ChangeBurnBoundsEvent(newMin, newMax);
    }

    // transfer and transferFrom are both dispatched to this function, so we
    // check blacklist and pay staking fee here.
    function transferAllArgsNoAllowance(address _from, address _to, uint256 _value) internal {
        require(!blackList.onList(_from));
        require(!blackList.onList(_to));
        super.transferAllArgsNoAllowance(_from, _to, _value);
        payStakingFee(_to, _value, transferFeeNumerator, transferFeeDenominator, 0, _from);
    }

    function wipeBlacklistedAccount(address account) public onlyOwner {
        require(blackList.onList(account));
        uint256 oldValue = balanceOf(account);
        balances.setBalance(account, 0);
        totalSupply_ = totalSupply_.sub(oldValue);
        WipedAccount(account, oldValue);
    }

    function payStakingFee(address payer, uint256 value, uint80 numerator, uint80 denominator, uint256 flatRate, address otherParticipant) private returns (uint256) {
        if (noFeesList.onList(payer) || noFeesList.onList(otherParticipant)) {
            return 0;
        }
        uint256 stakingFee = value.mul(numerator).div(denominator).add(flatRate);
        if (stakingFee > 0) {
            super.transferAllArgsNoAllowance(payer, staker, stakingFee);
        }
        return stakingFee;
    }

    function changeStakingFees(uint80 _transferFeeNumerator,
                                 uint80 _transferFeeDenominator,
                                 uint80 _mintFeeNumerator,
                                 uint80 _mintFeeDenominator,
                                 uint256 _mintFeeFlat,
                                 uint80 _burnFeeNumerator,
                                 uint80 _burnFeeDenominator,
                                 uint256 _burnFeeFlat) public onlyOwner {
        require(_transferFeeDenominator != 0);
        require(_mintFeeDenominator != 0);
        require(_burnFeeDenominator != 0);
        transferFeeNumerator = _transferFeeNumerator;
        transferFeeDenominator = _transferFeeDenominator;
        mintFeeNumerator = _mintFeeNumerator;
        mintFeeDenominator = _mintFeeDenominator;
        mintFeeFlat = _mintFeeFlat;
        burnFeeNumerator = _burnFeeNumerator;
        burnFeeDenominator = _burnFeeDenominator;
        burnFeeFlat = _burnFeeFlat;
    }

    function changeStaker(address newStaker) public onlyOwner {
        require(newStaker != address(0));
        staker = newStaker;
    }
}