pragma solidity ^0.5.0;


contract Context {
    // Empty internal constructor, to prevent people from mistakenly deploying
    // an instance of this contract, which should be used via inheritance.
    constructor () internal { }
    // solhint-disable-previous-line no-empty-blocks

    function _msgSender() internal view returns (address payable) {
        return msg.sender;
    }

    function _msgData() internal view returns (bytes memory) {
        this; // silence state mutability warning without generating bytecode - see https://github.com/ethereum/solidity/issues/2691
        return msg.data;
    }
}

interface IERC20 {
    /**
     * @dev Returns the amount of tokens in existence.
     */
    function totalSupply() external view returns (uint256);

    /**
     * @dev Returns the amount of tokens owned by `account`.
     */
    function balanceOf(address account) external view returns (uint256);

    /**
     * @dev Moves `amount` tokens from the caller's account to `recipient`.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * Emits a {Transfer} event.
     */
    function transfer(address recipient, uint256 amount) external returns (bool);

    /**
     * @dev Returns the remaining number of tokens that `spender` will be
     * allowed to spend on behalf of `owner` through {transferFrom}. This is
     * zero by default.
     *
     * This value changes when {approve} or {transferFrom} are called.
     */
    function allowance(address owner, address spender) external view returns (uint256);

    /**
     * @dev Sets `amount` as the allowance of `spender` over the caller's tokens.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * IMPORTANT: 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
     *
     * Emits an {Approval} event.
     */
    function approve(address spender, uint256 amount) external returns (bool);

    /**
     * @dev Moves `amount` tokens from `sender` to `recipient` using the
     * allowance mechanism. `amount` is then deducted from the caller's
     * allowance.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * Emits a {Transfer} event.
     */
    function transferFrom(address sender, address recipient, uint256 amount) external returns (bool);

    /**
     * @dev Emitted when `value` tokens are moved from one account (`from`) to
     * another (`to`).
     *
     * Note that `value` may be zero.
     */
    event Transfer(address indexed from, address indexed to, uint256 value);

    /**
     * @dev Emitted when the allowance of a `spender` for an `owner` is set by
     * a call to {approve}. `value` is the new allowance.
     */
    event Approval(address indexed owner, address indexed spender, uint256 value);
}

library SafeMath {
    /**
     * @dev Returns the addition of two unsigned integers, reverting on
     * overflow.
     *
     * Counterpart to Solidity's `+` operator.
     *
     * Requirements:
     * - Addition cannot overflow.
     */
    function add(uint256 a, uint256 b) internal pure returns (uint256) {
        uint256 c = a + b;
        require(c >= a, "SafeMath: addition overflow");

        return c;
    }

    /**
     * @dev Returns the subtraction of two unsigned integers, reverting on
     * overflow (when the result is negative).
     *
     * Counterpart to Solidity's `-` operator.
     *
     * Requirements:
     * - Subtraction cannot overflow.
     */
    function sub(uint256 a, uint256 b) internal pure returns (uint256) {
        return sub(a, b, "SafeMath: subtraction overflow");
    }

    /**
     * @dev Returns the subtraction of two unsigned integers, reverting with custom message on
     * overflow (when the result is negative).
     *
     * Counterpart to Solidity's `-` operator.
     *
     * Requirements:
     * - Subtraction cannot overflow.
     *
     * _Available since v2.4.0._
     */
    function sub(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b <= a, errorMessage);
        uint256 c = a - b;

        return c;
    }

    /**
     * @dev Returns the multiplication of two unsigned integers, reverting on
     * overflow.
     *
     * Counterpart to Solidity's `*` operator.
     *
     * Requirements:
     * - Multiplication cannot overflow.
     */
    function mul(uint256 a, uint256 b) internal pure returns (uint256) {
        // Gas optimization: this is cheaper than requiring 'a' not being zero, but the
        // benefit is lost if 'b' is also tested.
        // See: https://github.com/OpenZeppelin/openzeppelin-contracts/pull/522
        if (a == 0) {
            return 0;
        }

        uint256 c = a * b;
        require(c / a == b, "SafeMath: multiplication overflow");

        return c;
    }

    /**
     * @dev Returns the integer division of two unsigned integers. Reverts on
     * division by zero. The result is rounded towards zero.
     *
     * Counterpart to Solidity's `/` operator. Note: this function uses a
     * `revert` opcode (which leaves remaining gas untouched) while Solidity
     * uses an invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     * - The divisor cannot be zero.
     */
    function div(uint256 a, uint256 b) internal pure returns (uint256) {
        return div(a, b, "SafeMath: division by zero");
    }

    /**
     * @dev Returns the integer division of two unsigned integers. Reverts with custom message on
     * division by zero. The result is rounded towards zero.
     *
     * Counterpart to Solidity's `/` operator. Note: this function uses a
     * `revert` opcode (which leaves remaining gas untouched) while Solidity
     * uses an invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     * - The divisor cannot be zero.
     *
     * _Available since v2.4.0._
     */
    function div(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        // Solidity only automatically asserts when dividing by 0
        require(b > 0, errorMessage);
        uint256 c = a / b;
        // assert(a == b * c + a % b); // There is no case in which this doesn't hold

        return c;
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * Reverts when dividing by zero.
     *
     * Counterpart to Solidity's `%` operator. This function uses a `revert`
     * opcode (which leaves remaining gas untouched) while Solidity uses an
     * invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     * - The divisor cannot be zero.
     */
    function mod(uint256 a, uint256 b) internal pure returns (uint256) {
        return mod(a, b, "SafeMath: modulo by zero");
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * Reverts with custom message when dividing by zero.
     *
     * Counterpart to Solidity's `%` operator. This function uses a `revert`
     * opcode (which leaves remaining gas untouched) while Solidity uses an
     * invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     * - The divisor cannot be zero.
     *
     * _Available since v2.4.0._
     */
    function mod(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b != 0, errorMessage);
        return a % b;
    }
}

contract ERC20 is Context, IERC20 {
    using SafeMath for uint256;

    mapping (address => uint256) private _balances;

    mapping (address => mapping (address => uint256)) private _allowances;

    uint256 private _totalSupply;

    /**
     * @dev See {IERC20-totalSupply}.
     */
    function totalSupply() public view returns (uint256) {
        return _totalSupply;
    }

    /**
     * @dev See {IERC20-balanceOf}.
     */
    function balanceOf(address account) public view returns (uint256) {
        return _balances[account];
    }

    /**
     * @dev See {IERC20-transfer}.
     *
     * Requirements:
     *
     * - `recipient` cannot be the zero address.
     * - the caller must have a balance of at least `amount`.
     */
    function transfer(address recipient, uint256 amount) public returns (bool) {
        _transfer(_msgSender(), recipient, amount);
        return true;
    }

    /**
     * @dev See {IERC20-allowance}.
     */
    function allowance(address owner, address spender) public view returns (uint256) {
        return _allowances[owner][spender];
    }

    /**
     * @dev See {IERC20-approve}.
     *
     * Requirements:
     *
     * - `spender` cannot be the zero address.
     */
    function approve(address spender, uint256 amount) public returns (bool) {
        _approve(_msgSender(), spender, amount);
        return true;
    }

    /**
     * @dev See {IERC20-transferFrom}.
     *
     * Emits an {Approval} event indicating the updated allowance. This is not
     * required by the EIP. See the note at the beginning of {ERC20};
     *
     * Requirements:
     * - `sender` and `recipient` cannot be the zero address.
     * - `sender` must have a balance of at least `amount`.
     * - the caller must have allowance for `sender`'s tokens of at least
     * `amount`.
     */
    function transferFrom(address sender, address recipient, uint256 amount) public returns (bool) {
        _transfer(sender, recipient, amount);
        _approve(sender, _msgSender(), _allowances[sender][_msgSender()].sub(amount, "ERC20: transfer amount exceeds allowance"));
        return true;
    }

    /**
     * @dev Atomically increases the allowance granted to `spender` by the caller.
     *
     * This is an alternative to {approve} that can be used as a mitigation for
     * problems described in {IERC20-approve}.
     *
     * Emits an {Approval} event indicating the updated allowance.
     *
     * Requirements:
     *
     * - `spender` cannot be the zero address.
     */
    function increaseAllowance(address spender, uint256 addedValue) public returns (bool) {
        _approve(_msgSender(), spender, _allowances[_msgSender()][spender].add(addedValue));
        return true;
    }

    /**
     * @dev Atomically decreases the allowance granted to `spender` by the caller.
     *
     * This is an alternative to {approve} that can be used as a mitigation for
     * problems described in {IERC20-approve}.
     *
     * Emits an {Approval} event indicating the updated allowance.
     *
     * Requirements:
     *
     * - `spender` cannot be the zero address.
     * - `spender` must have allowance for the caller of at least
     * `subtractedValue`.
     */
    function decreaseAllowance(address spender, uint256 subtractedValue) public returns (bool) {
        _approve(_msgSender(), spender, _allowances[_msgSender()][spender].sub(subtractedValue, "ERC20: decreased allowance below zero"));
        return true;
    }

    /**
     * @dev Moves tokens `amount` from `sender` to `recipient`.
     *
     * This is internal function is equivalent to {transfer}, and can be used to
     * e.g. implement automatic token fees, slashing mechanisms, etc.
     *
     * Emits a {Transfer} event.
     *
     * Requirements:
     *
     * - `sender` cannot be the zero address.
     * - `recipient` cannot be the zero address.
     * - `sender` must have a balance of at least `amount`.
     */
    function _transfer(address sender, address recipient, uint256 amount) internal {
        require(sender != address(0), "ERC20: transfer from the zero address");
        require(recipient != address(0), "ERC20: transfer to the zero address");

        _balances[sender] = _balances[sender].sub(amount, "ERC20: transfer amount exceeds balance");
        _balances[recipient] = _balances[recipient].add(amount);
        emit Transfer(sender, recipient, amount);
    }

    /** @dev Creates `amount` tokens and assigns them to `account`, increasing
     * the total supply.
     *
     * Emits a {Transfer} event with `from` set to the zero address.
     *
     * Requirements
     *
     * - `to` cannot be the zero address.
     */
    function _mint(address account, uint256 amount) internal {
        require(account != address(0), "ERC20: mint to the zero address");

        _totalSupply = _totalSupply.add(amount);
        _balances[account] = _balances[account].add(amount);
        emit Transfer(address(0), account, amount);
    }

    /**
     * @dev Destroys `amount` tokens from `account`, reducing the
     * total supply.
     *
     * Emits a {Transfer} event with `to` set to the zero address.
     *
     * Requirements
     *
     * - `account` cannot be the zero address.
     * - `account` must have at least `amount` tokens.
     */
    function _burn(address account, uint256 amount) internal {
        require(account != address(0), "ERC20: burn from the zero address");

        _balances[account] = _balances[account].sub(amount, "ERC20: burn amount exceeds balance");
        _totalSupply = _totalSupply.sub(amount);
        emit Transfer(account, address(0), amount);
    }

    /**
     * @dev Sets `amount` as the allowance of `spender` over the `owner`s tokens.
     *
     * This is internal function is equivalent to `approve`, and can be used to
     * e.g. set automatic allowances for certain subsystems, etc.
     *
     * Emits an {Approval} event.
     *
     * Requirements:
     *
     * - `owner` cannot be the zero address.
     * - `spender` cannot be the zero address.
     */
    function _approve(address owner, address spender, uint256 amount) internal {
        require(owner != address(0), "ERC20: approve from the zero address");
        require(spender != address(0), "ERC20: approve to the zero address");

        _allowances[owner][spender] = amount;
        emit Approval(owner, spender, amount);
    }

    /**
     * @dev Destroys `amount` tokens from `account`.`amount` is then deducted
     * from the caller's allowance.
     *
     * See {_burn} and {_approve}.
     */
    function _burnFrom(address account, uint256 amount) internal {
        _burn(account, amount);
        _approve(account, _msgSender(), _allowances[account][_msgSender()].sub(amount, "ERC20: burn amount exceeds allowance"));
    }
}

library Roles {
    struct Role {
        mapping (address => bool) bearer;
    }

    /**
     * @dev Give an account access to this role.
     */
    function add(Role storage role, address account) internal {
        require(!has(role, account), "Roles: account already has role");
        role.bearer[account] = true;
    }

    /**
     * @dev Remove an account's access to this role.
     */
    function remove(Role storage role, address account) internal {
        require(has(role, account), "Roles: account does not have role");
        role.bearer[account] = false;
    }

    /**
     * @dev Check if an account has this role.
     * @return bool
     */
    function has(Role storage role, address account) internal view returns (bool) {
        require(account != address(0), "Roles: account is the zero address");
        return role.bearer[account];
    }
}

contract MinterRole is Context {
    using Roles for Roles.Role;

    event MinterAdded(address indexed account);
    event MinterRemoved(address indexed account);

    Roles.Role private _minters;

    constructor () internal {
        _addMinter(_msgSender());
    }

    modifier onlyMinter() {
        require(isMinter(_msgSender()), "MinterRole: caller does not have the Minter role");
        _;
    }

    function isMinter(address account) public view returns (bool) {
        return _minters.has(account);
    }

    function addMinter(address account) public onlyMinter {
        _addMinter(account);
    }

    function renounceMinter() public {
        _removeMinter(_msgSender());
    }

    function _addMinter(address account) internal {
        _minters.add(account);
        emit MinterAdded(account);
    }

    function _removeMinter(address account) internal {
        _minters.remove(account);
        emit MinterRemoved(account);
    }
}

contract ERC20Mintable is ERC20, MinterRole {
    /**
     * @dev See {ERC20-_mint}.
     *
     * Requirements:
     *
     * - the caller must have the {MinterRole}.
     */
    function mint(address account, uint256 amount) public onlyMinter returns (bool) {
        _mint(account, amount);
        return true;
    }
}

contract Ownable is Context {
    address private _owner;

    event OwnershipTransferred(address indexed previousOwner, address indexed newOwner);

    /**
     * @dev Initializes the contract setting the deployer as the initial owner.
     */
    constructor () internal {
        address msgSender = _msgSender();
        _owner = msgSender;
        emit OwnershipTransferred(address(0), msgSender);
    }

    /**
     * @dev Returns the address of the current owner.
     */
    function owner() public view returns (address) {
        return _owner;
    }

    /**
     * @dev Throws if called by any account other than the owner.
     */
    modifier onlyOwner() {
        require(isOwner(), "Ownable: caller is not the owner");
        _;
    }

    /**
     * @dev Returns true if the caller is the current owner.
     */
    function isOwner() public view returns (bool) {
        return _msgSender() == _owner;
    }

    /**
     * @dev Leaves the contract without owner. It will not be possible to call
     * `onlyOwner` functions anymore. Can only be called by the current owner.
     *
     * NOTE: Renouncing ownership will leave the contract without an owner,
     * thereby removing any functionality that is only available to the owner.
     */
    function renounceOwnership() public onlyOwner {
        emit OwnershipTransferred(_owner, address(0));
        _owner = address(0);
    }

    /**
     * @dev Transfers ownership of the contract to a new account (`newOwner`).
     * Can only be called by the current owner.
     */
    function transferOwnership(address newOwner) public onlyOwner {
        _transferOwnership(newOwner);
    }

    /**
     * @dev Transfers ownership of the contract to a new account (`newOwner`).
     */
    function _transferOwnership(address newOwner) internal {
        require(newOwner != address(0), "Ownable: new owner is the zero address");
        emit OwnershipTransferred(_owner, newOwner);
        _owner = newOwner;
    }
}

interface IInvestorRegistry {

    /**
     *  Add a verified address, along with an associated verification hash to the contract.
     *  Upon successful addition of a verified address, the contract must emit
     *  `VerifiedAddressAdded(addr, hash, msg.sender)`.
     *  It MUST throw if the supplied address or hash are zero, or if the address has already been supplied.
     *  @param addr The address of the person represented by the supplied hash.
     *  @param hash A cryptographic hash of the address holder's verified information.
     */
    function addVerified(address addr, bytes32 hash) external;

    /**
     *  Update the hash for a verified address known to the contract.
     *  Upon successful update of a verified address the contract must emit
     *  `VerifiedAddressUpdated(addr, oldHash, hash, msg.sender)`.
     *  If the hash is the same as the value already stored then
     *  no `VerifiedAddressUpdated` event is to be emitted.
     *  It MUST throw if the hash is zero, or if the address is unverified.
     *  @param addr The verified address of the person represented by the supplied hash.
     *  @param hash A new cryptographic hash of the address holder's updated verified information.
     */
    function updateVerified(address addr, bytes32 hash) external;

    /**
     *  Tests that the supplied address is known to the contract.
     *  @param addr The address to test.
     *  @return true if the address is known to the contract.
     */
    function isVerified(address addr) external view returns (bool);

    /**
     *  Tests that the supplied address is known and not cancelled.
     *  @param addr The address to test.
     *  @return true if the address is known to the contract.
     */
    // function isNotCancelled(address addr) external returns (bool);

    /**
     *  Checks that the supplied hash is associated with the given address.
     *  @param addr The address to test.
     *  @param hash The hash to test.
     *  @return true if the hash matches the one supplied with the address in `addVerified`, or `updateVerified`.
     */
    function hasHash(address addr, bytes32 hash) external view returns (bool);

    /**
     *  Checks to see if the supplied address was superseded.
     *  @param addr The address to check.
     *  @return true if the supplied address was superseded by another address.
     */
    function isSuperseded(address addr) external view returns (bool);

    /**
     *  Gets the most recent address, given a superseded one.
     *  Addresses may be superseded multiple times, so this function needs to
     *  follow the chain of addresses until it reaches the final, verified address.
     *  @param addr The superseded address.
     *  @return the verified address that ultimately holds the share.
     */
    function getCurrentFor(address addr) external view returns (address);

}

contract PlusBioToken is ERC20Mintable, Ownable {

    string public name;
    string public symbol;

    uint public decimals = 2;

    // Investor Registry Contract
    IInvestorRegistry investorRegistryContract;

    /**
     *  This is the constructor which registers the name and symbol
     *  @param _name The token name
     *  @param _symbol The token symbol
     */
    constructor(string memory _name, string memory _symbol) public {
        name = _name;
        symbol = _symbol;
    }

    bytes32 constant private ZERO_BYTES = bytes32(0);
    address constant private ZERO_ADDRESS = address(0);


    /**
     *  This event is emitted when an address is cancelled and replaced with
     *  a new address.  This happens in the case where a shareholder has
     *  lost access to their original address and needs to have their share
     *  reissued to a new address.  This is the equivalent of issuing replacement
     *  share certificates.
     *  @param original The address being superseded.
     *  @param replacement The new address.
     *  @param sender The address that caused the address to be superseded.
     */
     event VerifiedAddressSuperseded(
        address indexed original,
        address indexed replacement,
        address indexed sender
        );

    /**
     *  This event is emitted when the registry address is set or modifiec.
     *  @param addr The address of the investor registry contract
     */
    event InvestorRegistrySet(
        address indexed addr
        );

    // Mappings
    mapping(address => uint256) private holderIndices;

    // Shareholders array
    address[] private shareholders;

    // Investor Registry Contract
    address private _investorRegistryAddress;

    modifier isVerifiedAddress(address addr) {
        require(investorRegistryContract.isVerified(addr), "not verified");
        _;
    }

    modifier isShareholder(address addr) {
        require(holderIndices[addr] != 0, "not a shareholder");
        _;
    }

    modifier isNotShareholder(address addr) {
        require(holderIndices[addr] == 0, "is a shareolder");
        _;
    }

    modifier hasRegistry() {
        require(_investorRegistryAddress != ZERO_ADDRESS, "investor registry not set");
        _;
    }

    /**
     *  Set the Investors Registry Contract address.
     *  Upon successful modification of address, the contract must emit
     *  `InvestorRegistrySet(addr)`.
     *  It MUST throw if the supplied address or hash are zero, or if the address has already been supplied.
     *  @param addr The address of the person represented by the supplied hash.
     */
    function setInvestorRegistry(address addr)
        public
        onlyOwner
    {
        require(addr != ZERO_ADDRESS, "address should not be zero");
        require(addr != _investorRegistryAddress, "address already be issued");
        investorRegistryContract = IInvestorRegistry(addr);
        _investorRegistryAddress = addr;
        emit InvestorRegistrySet(addr);
    }

    /**
    * @return the address of the Investor Registry Contract.
    */
    function investorRegistry() public view returns(address) {
        return _investorRegistryAddress;
    }

    /**
     * As each token is minted it is added to the shareholders array.
     * @param _to The address that will receive the minted tokens.
     * @param _amount The amount of tokens to mint.
     * @return A boolean that indicates if the operation was successful.
     */
    function mint(address _to, uint256 _amount)
        public
        onlyMinter
        hasRegistry
        isVerifiedAddress(_to)
        returns (bool)
    {
        // if the address does not already own share then
        // add the address to the shareholders array and record the index.
        updateShareholders(_to);
        return super.mint(_to, _amount);
    }

    /**
     *  The number of addresses that own tokens.
     *  @return the number of unique addresses that own tokens.
     */
    function holderCount()
        public
        onlyMinter
        view
        returns (uint)
    {
        return shareholders.length;
    }

    /**
     *  By counting the number of token holders using `holderCount`
     *  you can retrieve the complete list of token holders, one at a time.
     *  It MUST throw if `index >= holderCount()`.
     *  @param index The zero-based index of the holder.
     *  @return the address of the token holder with the given index.
     */
    function holderAt(uint256 index)
        public
        onlyMinter
        view
        returns (address)
    {
        require(index < shareholders.length, "index out of bound");
        return shareholders[index];
    }

    /**
     *  The `transfer` function MUST NOT allow transfers to addresses that
     *  have not been verified and added to the contract.
     *  If the `to` address is not currently a shareholder then it MUST become one.
     *  If the transfer will reduce `msg.sender`'s balance to 0 then that address
     *  MUST be removed from the list of shareholders.
     */
    function transfer(address to, uint256 value)
        public
        isVerifiedAddress(to)
        returns (bool)
    {
        updateShareholders(to);
        pruneShareholders(msg.sender, value);
        return super.transfer(to, value);
    }

    /**
     *  The `transferFrom` function MUST NOT allow transfers to addresses that
     *  have not been verified and added to the contract.
     *  If the `to` address is not currently a shareholder then it MUST become one.
     *  If the transfer will reduce `from`'s balance to 0 then that address
     *  MUST be removed from the list of shareholders.
     */
    function transferFrom(address from, address to, uint256 value)
        public
        isVerifiedAddress(to)
        returns (bool)
    {
        updateShareholders(to);
        pruneShareholders(from, value);
        return super.transferFrom(from, to, value);
    }

    /**
     *  Checks to see if the supplied address is a share holder.
     *  @param addr The address to check.
     *  @return true if the supplied address owns a token.
     */
    function isHolder(address addr)
        public
        view
        returns (bool)
    {
        return holderIndices[addr] != 0;
    }

    /**
     *  If the address is not in the `shareholders` array then push it
     *  and update the `holderIndices` mapping.
     *  @param addr The address to add as a shareholder if it's not already.
     */
    function updateShareholders(address addr) internal {
        if (holderIndices[addr] == 0) {
            holderIndices[addr] = shareholders.push(addr);
        }
    }

    /**
     *  If the address is in the `shareholders` array and the forthcoming
     *  transfer or transferFrom will reduce their balance to 0, then
     *  we need to remove them from the shareholders array.
     *  @param addr The address to prune if their balance will be reduced to 0.
     @  @dev see https://ethereum.stackexchange.com/a/39311
     */
    function pruneShareholders(address addr, uint256 value) internal {
        uint256 balance = balanceOf(addr) - value;
        if (balance > 0) {
            return;
        }
        uint256 holderIndex = holderIndices[addr] - 1;
        uint256 lastIndex = shareholders.length - 1;
        address lastHolder = shareholders[lastIndex];
        // overwrite the addr's slot with the last shareholder
        shareholders[holderIndex] = lastHolder;
        // also copy over the index (thanks @mohoff for spotting this)
        // ref https://github.com/davesag/ERC884-reference-implementation/issues/20
        holderIndices[lastHolder] = holderIndices[addr];
        // trim the shareholders array (which drops the last entry)
        shareholders.length--;
        // and zero out the index for addr
        holderIndices[addr] = 0;
    }

}