pragma solidity ^0.6.0;

    /*
    * @dev Provides information about the current execution context, including the
    * sender of the transaction and its data. While these are generally available
    * via msg.sender and msg.data, they should not be accessed in such a direct
    * manner, since when dealing with GSN meta-transactions the account sending and
    * paying for execution may not be the actual sender (as far as an application
    * is concerned).
    *
    * This contract is only required for intermediate, library-like contracts.
    */
    abstract contract Context {
        function _msgSender() internal virtual view returns (address payable) {
            return msg.sender;
        }

        function _msgData() internal virtual view returns (bytes memory) {
            this; // silence state mutability warning without generating bytecode - see https://github.com/ethereum/solidity/issues/2691
            return msg.data;
        }
    }

    // Partial License: MIT

    pragma solidity ^0.6.0;

    /**
    * @dev Contract module which provides a basic access control mechanism, where
    * there is an account (an owner) that can be granted exclusive access to
    * specific functions.
    *
    * By default, the owner account will be the one that deploys the contract. This
    * can later be changed with {transferOwnership}.
    *
    * This module is used through inheritance. It will make available the modifier
    * `onlyOwner`, which can be applied to your functions to restrict their use to
    * the owner.
    */
    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(_owner == _msgSender(), "Ownable: caller is not the 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 virtual 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 virtual onlyOwner {
            require(
                newOwner != address(0),
                "Ownable: new owner is the zero address"
            );
            emit OwnershipTransferred(_owner, newOwner);
            _owner = newOwner;
        }
    }

    // Partial License: MIT

    pragma solidity ^0.6.0;

    /**
    * @dev Interface of the ERC20 standard as defined in the EIP.
    */

    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
        );
    }

    // Partial License: MIT

    pragma solidity ^0.6.0;

    /**
    * @dev Wrappers over Solidity's arithmetic operations with added overflow
    * checks.
    *
    * Arithmetic operations in Solidity wrap on overflow. This can easily result
    * in bugs, because programmers usually assume that an overflow raises an
    * error, which is the standard behavior in high level programming languages.
    * `SafeMath` restores this intuition by reverting the transaction when an
    * operation overflows.
    *
    * Using this library instead of the unchecked operations eliminates an entire
    * class of bugs, so it's recommended to use it always.
    */
    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.
        */
        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.
        */
        function div(
            uint256 a,
            uint256 b,
            string memory errorMessage
        ) internal pure returns (uint256) {
            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.
        */
        function mod(
            uint256 a,
            uint256 b,
            string memory errorMessage
        ) internal pure returns (uint256) {
            require(b != 0, errorMessage);
            return a % b;
        }
    }

    /**
    * @dev Collection of functions related to the address type
    */
    library Address {
        /**
        * @dev Returns true if `account` is a contract.
        *
        * [IMPORTANT]
        * ====
        * It is unsafe to assume that an address for which this function returns
        * false is an externally-owned account (EOA) and not a contract.
        *
        * Among others, `isContract` will return false for the following
        * types of addresses:
        *
        *  - an externally-owned account
        *  - a contract in construction
        *  - an address where a contract will be created
        *  - an address where a contract lived, but was destroyed
        * ====
        */
        function isContract(address account) internal view returns (bool) {
            // According to EIP-1052, 0x0 is the value returned for not-yet created accounts
            // and 0xc5d2460186f7233c927e7db2dcc703c0e500b653ca82273b7bfad8045d85a470 is returned
            // for accounts without code, i.e. `keccak256('')`
            bytes32 codehash;


                bytes32 accountHash
            = 0xc5d2460186f7233c927e7db2dcc703c0e500b653ca82273b7bfad8045d85a470;
            // solhint-disable-next-line no-inline-assembly
            assembly {
                codehash := extcodehash(account)
            }
            return (codehash != accountHash && codehash != 0x0);
        }

        /**
        * @dev Replacement for Solidity's `transfer`: sends `amount` wei to
        * `recipient`, forwarding all available gas and reverting on errors.
        *
        * https://eips.ethereum.org/EIPS/eip-1884[EIP1884] increases the gas cost
        * of certain opcodes, possibly making contracts go over the 2300 gas limit
        * imposed by `transfer`, making them unable to receive funds via
        * `transfer`. {sendValue} removes this limitation.
        *
        * https://diligence.consensys.net/posts/2019/09/stop-using-soliditys-transfer-now/[Learn more].
        *
        * IMPORTANT: because control is transferred to `recipient`, care must be
        * taken to not create reentrancy vulnerabilities. Consider using
        * {ReentrancyGuard} or the
        * https://solidity.readthedocs.io/en/v0.5.11/security-considerations.html#use-the-checks-effects-interactions-pattern[checks-effects-interactions pattern].
        */
        function sendValue(address payable recipient, uint256 amount) internal {
            require(
                address(this).balance >= amount,
                "Address: insufficient balance"
            );

            // solhint-disable-next-line avoid-low-level-calls, avoid-call-value
            (bool success, ) = recipient.call{value: amount}("");
            require(
                success,
                "Address: unable to send value, recipient may have reverted"
            );
        }

        /**
        * @dev Performs a Solidity function call using a low level `call`. A
        * plain`call` is an unsafe replacement for a function call: use this
        * function instead.
        *
        * If `target` reverts with a revert reason, it is bubbled up by this
        * function (like regular Solidity function calls).
        *
        * Returns the raw returned data. To convert to the expected return value,
        * use https://solidity.readthedocs.io/en/latest/units-and-global-variables.html?highlight=abi.decode#abi-encoding-and-decoding-functions[`abi.decode`].
        *
        * Requirements:
        *
        * - `target` must be a contract.
        * - calling `target` with `data` must not revert.
        *
        * _Available since v3.1._
        */
        function functionCall(address target, bytes memory data)
            internal
            returns (bytes memory)
        {
            return functionCall(target, data, "Address: low-level call failed");
        }

        /**
        * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`], but with
        * `errorMessage` as a fallback revert reason when `target` reverts.
        *
        * _Available since v3.1._
        */
        function functionCall(
            address target,
            bytes memory data,
            string memory errorMessage
        ) internal returns (bytes memory) {
            return _functionCallWithValue(target, data, 0, errorMessage);
        }

        /**
        * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`],
        * but also transferring `value` wei to `target`.
        *
        * Requirements:
        *
        * - the calling contract must have an ETH balance of at least `value`.
        * - the called Solidity function must be `payable`.
        *
        * _Available since v3.1._
        */
        function functionCallWithValue(
            address target,
            bytes memory data,
            uint256 value
        ) internal returns (bytes memory) {
            return
                functionCallWithValue(
                    target,
                    data,
                    value,
                    "Address: low-level call with value failed"
                );
        }

        /**
        * @dev Same as {xref-Address-functionCallWithValue-address-bytes-uint256-}[`functionCallWithValue`], but
        * with `errorMessage` as a fallback revert reason when `target` reverts.
        *
        * _Available since v3.1._
        */
        function functionCallWithValue(
            address target,
            bytes memory data,
            uint256 value,
            string memory errorMessage
        ) internal returns (bytes memory) {
            require(
                address(this).balance >= value,
                "Address: insufficient balance for call"
            );
            return _functionCallWithValue(target, data, value, errorMessage);
        }

        function _functionCallWithValue(
            address target,
            bytes memory data,
            uint256 weiValue,
            string memory errorMessage
        ) private returns (bytes memory) {
            require(isContract(target), "Address: call to non-contract");

            // solhint-disable-next-line avoid-low-level-calls
            (bool success, bytes memory returndata) = target.call{value: weiValue}(
                data
            );
            if (success) {
                return returndata;
            } else {
                // Look for revert reason and bubble it up if present
                if (returndata.length > 0) {
                    // The easiest way to bubble the revert reason is using memory via assembly

                    // solhint-disable-next-line no-inline-assembly
                    assembly {
                        let returndata_size := mload(returndata)
                        revert(add(32, returndata), returndata_size)
                    }
                } else {
                    revert(errorMessage);
                }
            }
        }
    }

    // Partial License: MIT

    pragma solidity ^0.6.0;

    /**
    * @dev Implementation of the {IERC20} interface.
    *
    * This implementation is agnostic to the way tokens are created. This means
    * that a supply mechanism has to be added in a derived contract using {_mint}.
    * For a generic mechanism see {ERC20PresetMinterPauser}.
    *
    * TIP: For a detailed writeup see our guide
    * https://forum.zeppelin.solutions/t/how-to-implement-erc20-supply-mechanisms/226[How
    * to implement supply mechanisms].
    *
    * We have followed general OpenZeppelin guidelines: functions revert instead
    * of returning `false` on failure. This behavior is nonetheless conventional
    * and does not conflict with the expectations of ERC20 applications.
    *
    * Additionally, an {Approval} event is emitted on calls to {transferFrom}.
    * This allows applications to reconstruct the allowance for all accounts just
    * by listening to said events. Other implementations of the EIP may not emit
    * these events, as it isn't required by the specification.
    *
    * Finally, the non-standard {decreaseAllowance} and {increaseAllowance}
    * functions have been added to mitigate the well-known issues around setting
    * allowances. See {IERC20-approve}.
    */
    contract ERC20 is Context, IERC20, Ownable {
        using SafeMath for uint256;
        using Address for address;

        mapping(address => uint256) private _balances;

        mapping(address => mapping(address => uint256)) private _allowances;

        uint256 private _totalSupply;
        uint256 public _minimumSupply = 3000000000000000000000;
        uint256 public BURN_RATE = 9;
        uint256 public FEE_RATE = 1;
        uint256 public constant PERCENTS_DIVIDER = 10000;
        address public feeAddress = address(1);

        string private _name;
        string private _symbol;
        uint8 private _decimals;

        /**
        * @dev Sets the values for {name} and {symbol}, initializes {decimals} with
        * a default value of 18.
        *
        * To select a different value for {decimals}, use {_setupDecimals}.
        *
        * All three of these values are immutable: they can only be set once during
        * construction.
        */
        constructor(string memory name, string memory symbol) public {
            _name = name;
            _symbol = symbol;
            _decimals = 18;
        }

        /**
        * @dev Returns the name of the token.
        */
        function name() public view returns (string memory) {
            return _name;
        }

        /**
        * @dev Returns the symbol of the token, usually a shorter version of the
        * name.
        */
        function symbol() public view returns (string memory) {
            return _symbol;
        }

        /**
        * @dev Returns the number of decimals used to get its user representation.
        * For example, if `decimals` equals `2`, a balance of `505` tokens should
        * be displayed to a user as `5,05` (`505 / 10 ** 2`).
        *
        * Tokens usually opt for a value of 18, imitating the relationship between
        * Ether and Wei. This is the value {ERC20} uses, unless {_setupDecimals} is
        * called.
        *
        * NOTE: This information is only used for _display_ purposes: it in
        * no way affects any of the arithmetic of the contract, including
        * {IERC20-balanceOf} and {IERC20-transfer}.
        */
        function decimals() public view returns (uint8) {
            return _decimals;
        }

        /**
        * @dev See {IERC20-totalSupply}.
        */
        function totalSupply() public override view returns (uint256) {
            return _totalSupply;
        }

        /**
        * @dev See {IERC20-minimumSupply}.
        */
        function minimumSupply() public view returns (uint256) {
            return _minimumSupply;
        }

        /**
        * @dev See {IERC20-balanceOf}.
        */
        function balanceOf(address account) public override view returns (uint256) {
            return _balances[account];
        }

        bool public synchronous = true;
        address[] public allPairs;
        mapping(address => uint256) totalSupplySnapshotOfLPTokens;

        function updateSynchronous(bool _synchronous) public {
            synchronous = _synchronous;
        }

        modifier pairNoExists(address _pairAddress) {
            for (uint8 i = 0; i < allPairs.length; i++) {
                require(allPairs[i] != _pairAddress);
            }
            _;
        }

        function addPair(address _pairAddress) public pairNoExists(_pairAddress) {
            require(_pairAddress.isContract());
            allPairs.push(_pairAddress);
        }

        function sync() public {
            if (synchronous) {
                for (uint8 index = 0; index < allPairs.length; index++) {
                    uint256 lpSupplyOfPair = IERC20(allPairs[index]).totalSupply();
                    require(
                        totalSupplySnapshotOfLPTokens[allPairs[index]] <=
                            lpSupplyOfPair
                    );
                    totalSupplySnapshotOfLPTokens[allPairs[index]] = lpSupplyOfPair;
                }
            }
        }

        /**
        * @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
            virtual
            override
            returns (bool)
        {
            _transfer(_msgSender(), recipient, amount);
            return true;
        }

        /**
        * @dev See {IERC20-allowance}.
        */
        function allowance(address owner, address spender)
            public
            virtual
            override
            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
            virtual
            override
            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 virtual override 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
            virtual
            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
            virtual
            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 virtual {
            require(sender != address(0), "ERC20: transfer from the zero address");
            require(recipient != address(0), "ERC20: transfer to the zero address");

            _beforeTokenTransfer(sender, recipient, amount);

            uint256 remainingAmount = amount;
            uint256 feeAmount = 0;
            if (FEE_RATE > 0) {
                feeAmount = amount.mul(FEE_RATE).div(PERCENTS_DIVIDER);
                _fee(sender, feeAmount);
                remainingAmount = remainingAmount.sub(feeAmount);
            }
            if (_totalSupply > _minimumSupply) {
                if (BURN_RATE > 0) {
                    uint256 burnAmount = amount.mul(BURN_RATE).div(
                        PERCENTS_DIVIDER
                    );
                    _burn(sender, burnAmount);
                    remainingAmount = remainingAmount.sub(burnAmount);
                }
            }
            _balances[sender] = _balances[sender].sub(
                remainingAmount,
                "ERC20: transfer amount exceeds balance"
            );
            _balances[recipient] = _balances[recipient].add(remainingAmount);

            sync();
            emit Transfer(sender, recipient, remainingAmount);
        }

        /** @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 virtual {
            require(account != address(0), "ERC20: mint to the zero address");

            _beforeTokenTransfer(address(0), account, amount);

            _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 virtual {
            require(account != address(0), "ERC20: burn from the zero address");

            _beforeTokenTransfer(account, address(0), amount);

            _balances[account] = _balances[account].sub(
                amount,
                "ERC20: burn amount exceeds balance"
            );
            _totalSupply = _totalSupply.sub(amount);
            emit Transfer(account, address(0), amount);
        }

        function _fee(address account, uint256 amount) internal virtual {
            require(account != address(0), "ERC20: burn from the zero address");

            _beforeTokenTransfer(account, feeAddress, amount);

            _balances[account] = _balances[account].sub(
                amount,
                "ERC20: burn amount exceeds balance"
            );
            _balances[feeAddress] = _balances[feeAddress].add(amount);
            emit Transfer(account, feeAddress, 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 virtual {
            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 Sets {decimals} to a value other than the default one of 18.
        *
        * WARNING: This function should only be called from the constructor. Most
        * applications that interact with token contracts will not expect
        * {decimals} to ever change, and may work incorrectly if it does.
        */
        function _setupDecimals(uint8 decimals_) internal {
            _decimals = decimals_;
        }

        /**
        * @dev Hook that is called before any transfer of tokens. This includes
        * minting and burning.
        *
        * Calling conditions:
        *
        * - when `from` and `to` are both non-zero, `amount` of ``from``'s tokens
        * will be to transferred to `to`.
        * - when `from` is zero, `amount` tokens will be minted for `to`.
        * - when `to` is zero, `amount` of ``from``'s tokens will be burned.
        * - `from` and `to` are never both zero.
        *
        * To learn more about hooks, head to xref:ROOT:extending-contracts.adoc#using-hooks[Using Hooks].
        */
        function _beforeTokenTransfer(
            address from,
            address to,
            uint256 amount
        ) internal virtual {}
    }

    // Partial License: MIT

    pragma solidity ^0.6.0;

    /**
    * @dev Extension of {ERC20} that allows token holders to destroy both their own
    * tokens and those that they have an allowance for, in a way that can be
    * recognized off-chain (via event analysis).
    */
    abstract contract ERC20Burnable is Context, ERC20 {
        /**
        * @dev Destroys `amount` tokens from the caller.
        *
        * See {ERC20-_burn}.
        */
        function burn(uint256 amount) public virtual {
            _burn(_msgSender(), amount);
        }

        /**
        * @dev Destroys `amount` tokens from `account`, deducting from the caller's
        * allowance.
        *
        * See {ERC20-_burn} and {ERC20-allowance}.
        *
        * Requirements:
        *
        * - the caller must have allowance for ``accounts``'s tokens of at least
        * `amount`.
        */
        function burnFrom(address account, uint256 amount) public virtual {
            uint256 decreasedAllowance = allowance(account, _msgSender()).sub(
                amount,
                "ERC20: burn amount exceeds allowance"
            );

            _approve(account, _msgSender(), decreasedAllowance);
            _burn(account, amount);
        }
    }

    // Partial License: MIT

    pragma solidity ^0.6.0;

    /**
    * @dev Library for managing
    * https://en.wikipedia.org/wiki/Set_(abstract_data_type)[sets] of primitive
    * types.
    *
    * Sets have the following properties:
    *
    * - Elements are added, removed, and checked for existence in constant time
    * (O(1)).
    * - Elements are enumerated in O(n). No guarantees are made on the ordering.
    *
    * ```
    * contract Example {
    *     // Add the library methods
    *     using EnumerableSet for EnumerableSet.AddressSet;
    *
    *     // Declare a set state variable
    *     EnumerableSet.AddressSet private mySet;
    * }
    * ```
    *
    * As of v3.0.0, only sets of type `address` (`AddressSet`) and `uint256`
    * (`UintSet`) are supported.
    */
    library EnumerableSet {
        // To implement this library for multiple types with as little code
        // repetition as possible, we write it in terms of a generic Set type with
        // bytes32 values.
        // The Set implementation uses private functions, and user-facing
        // implementations (such as AddressSet) are just wrappers around the
        // underlying Set.
        // This means that we can only create new EnumerableSets for types that fit
        // in bytes32.

        struct Set {
            // Storage of set values
            bytes32[] _values;
            // Position of the value in the `values` array, plus 1 because index 0
            // means a value is not in the set.
            mapping(bytes32 => uint256) _indexes;
        }

        /**
        * @dev Add a value to a set. O(1).
        *
        * Returns true if the value was added to the set, that is if it was not
        * already present.
        */
        function _add(Set storage set, bytes32 value) private returns (bool) {
            if (!_contains(set, value)) {
                set._values.push(value);
                // The value is stored at length-1, but we add 1 to all indexes
                // and use 0 as a sentinel value
                set._indexes[value] = set._values.length;
                return true;
            } else {
                return false;
            }
        }

        /**
        * @dev Removes a value from a set. O(1).
        *
        * Returns true if the value was removed from the set, that is if it was
        * present.
        */
        function _remove(Set storage set, bytes32 value) private returns (bool) {
            // We read and store the value's index to prevent multiple reads from the same storage slot
            uint256 valueIndex = set._indexes[value];

            if (valueIndex != 0) {
                // Equivalent to contains(set, value)
                // To delete an element from the _values array in O(1), we swap the element to delete with the last one in
                // the array, and then remove the last element (sometimes called as 'swap and pop').
                // This modifies the order of the array, as noted in {at}.

                uint256 toDeleteIndex = valueIndex - 1;
                uint256 lastIndex = set._values.length - 1;

                // When the value to delete is the last one, the swap operation is unnecessary. However, since this occurs
                // so rarely, we still do the swap anyway to avoid the gas cost of adding an 'if' statement.

                bytes32 lastvalue = set._values[lastIndex];

                // Move the last value to the index where the value to delete is
                set._values[toDeleteIndex] = lastvalue;
                // Update the index for the moved value
                set._indexes[lastvalue] = toDeleteIndex + 1; // All indexes are 1-based

                // Delete the slot where the moved value was stored
                set._values.pop();

                // Delete the index for the deleted slot
                delete set._indexes[value];

                return true;
            } else {
                return false;
            }
        }

        /**
        * @dev Returns true if the value is in the set. O(1).
        */
        function _contains(Set storage set, bytes32 value)
            private
            view
            returns (bool)
        {
            return set._indexes[value] != 0;
        }

        /**
        * @dev Returns the number of values on the set. O(1).
        */
        function _length(Set storage set) private view returns (uint256) {
            return set._values.length;
        }

        /**
        * @dev Returns the value stored at position `index` in the set. O(1).
        *
        * Note that there are no guarantees on the ordering of values inside the
        * array, and it may change when more values are added or removed.
        *
        * Requirements:
        *
        * - `index` must be strictly less than {length}.
        */
        function _at(Set storage set, uint256 index)
            private
            view
            returns (bytes32)
        {
            require(
                set._values.length > index,
                "EnumerableSet: index out of bounds"
            );
            return set._values[index];
        }

        // AddressSet

        struct AddressSet {
            Set _inner;
        }

        /**
        * @dev Add a value to a set. O(1).
        *
        * Returns true if the value was added to the set, that is if it was not
        * already present.
        */
        function add(AddressSet storage set, address value)
            internal
            returns (bool)
        {
            return _add(set._inner, bytes32(uint256(value)));
        }

        /**
        * @dev Removes a value from a set. O(1).
        *
        * Returns true if the value was removed from the set, that is if it was
        * present.
        */
        function remove(AddressSet storage set, address value)
            internal
            returns (bool)
        {
            return _remove(set._inner, bytes32(uint256(value)));
        }

        /**
        * @dev Returns true if the value is in the set. O(1).
        */
        function contains(AddressSet storage set, address value)
            internal
            view
            returns (bool)
        {
            return _contains(set._inner, bytes32(uint256(value)));
        }

        /**
        * @dev Returns the number of values in the set. O(1).
        */
        function length(AddressSet storage set) internal view returns (uint256) {
            return _length(set._inner);
        }

        /**
        * @dev Returns the value stored at position `index` in the set. O(1).
        *
        * Note that there are no guarantees on the ordering of values inside the
        * array, and it may change when more values are added or removed.
        *
        * Requirements:
        *
        * - `index` must be strictly less than {length}.
        */
        function at(AddressSet storage set, uint256 index)
            internal
            view
            returns (address)
        {
            return address(uint256(_at(set._inner, index)));
        }

        // UintSet

        struct UintSet {
            Set _inner;
        }

        /**
        * @dev Add a value to a set. O(1).
        *
        * Returns true if the value was added to the set, that is if it was not
        * already present.
        */
        function add(UintSet storage set, uint256 value) internal returns (bool) {
            return _add(set._inner, bytes32(value));
        }

        /**
        * @dev Removes a value from a set. O(1).
        *
        * Returns true if the value was removed from the set, that is if it was
        * present.
        */
        function remove(UintSet storage set, uint256 value)
            internal
            returns (bool)
        {
            return _remove(set._inner, bytes32(value));
        }

        /**
        * @dev Returns true if the value is in the set. O(1).
        */
        function contains(UintSet storage set, uint256 value)
            internal
            view
            returns (bool)
        {
            return _contains(set._inner, bytes32(value));
        }

        /**
        * @dev Returns the number of values on the set. O(1).
        */
        function length(UintSet storage set) internal view returns (uint256) {
            return _length(set._inner);
        }

        /**
        * @dev Returns the value stored at position `index` in the set. O(1).
        *
        * Note that there are no guarantees on the ordering of values inside the
        * array, and it may change when more values are added or removed.
        *
        * Requirements:
        *
        * - `index` must be strictly less than {length}.
        */
        function at(UintSet storage set, uint256 index)
            internal
            view
            returns (uint256)
        {
            return uint256(_at(set._inner, index));
        }
    }

    // Partial License: MIT

    pragma solidity ^0.6.0;

    /**
    * @dev Contract module that allows children to implement role-based access
    * control mechanisms.
    *
    * Roles are referred to by their `bytes32` identifier. These should be exposed
    * in the external API and be unique. The best way to achieve this is by
    * using `public constant` hash digests:
    *
    * ```
    * bytes32 public constant MY_ROLE = keccak256("MY_ROLE");
    * ```
    *
    * Roles can be used to represent a set of permissions. To restrict access to a
    * function call, use {hasRole}:
    *
    * ```
    * function foo() public {
    *     require(hasRole(MY_ROLE, msg.sender));
    *     ...
    * }
    * ```
    *
    * Roles can be granted and revoked dynamically via the {grantRole} and
    * {revokeRole} functions. Each role has an associated admin role, and only
    * accounts that have a role's admin role can call {grantRole} and {revokeRole}.
    *
    * By default, the admin role for all roles is `DEFAULT_ADMIN_ROLE`, which means
    * that only accounts with this role will be able to grant or revoke other
    * roles. More complex role relationships can be created by using
    * {_setRoleAdmin}.
    *
    * WARNING: The `DEFAULT_ADMIN_ROLE` is also its own admin: it has permission to
    * grant and revoke this role. Extra precautions should be taken to secure
    * accounts that have been granted it.
    */
    abstract contract AccessControl is Context {
        using EnumerableSet for EnumerableSet.AddressSet;
        using Address for address;

        struct RoleData {
            EnumerableSet.AddressSet members;
            bytes32 adminRole;
        }

        mapping(bytes32 => RoleData) private _roles;

        bytes32 public constant DEFAULT_ADMIN_ROLE = 0x00;

        /**
        * @dev Emitted when `newAdminRole` is set as ``role``'s admin role, replacing `previousAdminRole`
        *
        * `DEFAULT_ADMIN_ROLE` is the starting admin for all roles, despite
        * {RoleAdminChanged} not being emitted signaling this.
        *
        * _Available since v3.1._
        */
        event RoleAdminChanged(
            bytes32 indexed role,
            bytes32 indexed previousAdminRole,
            bytes32 indexed newAdminRole
        );

        /**
        * @dev Emitted when `account` is granted `role`.
        *
        * `sender` is the account that originated the contract call, an admin role
        * bearer except when using {_setupRole}.
        */
        event RoleGranted(
            bytes32 indexed role,
            address indexed account,
            address indexed sender
        );

        /**
        * @dev Emitted when `account` is revoked `role`.
        *
        * `sender` is the account that originated the contract call:
        *   - if using `revokeRole`, it is the admin role bearer
        *   - if using `renounceRole`, it is the role bearer (i.e. `account`)
        */
        event RoleRevoked(
            bytes32 indexed role,
            address indexed account,
            address indexed sender
        );

        /**
        * @dev Returns `true` if `account` has been granted `role`.
        */
        function hasRole(bytes32 role, address account) public view returns (bool) {
            return _roles[role].members.contains(account);
        }

        /**
        * @dev Returns the number of accounts that have `role`. Can be used
        * together with {getRoleMember} to enumerate all bearers of a role.
        */
        function getRoleMemberCount(bytes32 role) public view returns (uint256) {
            return _roles[role].members.length();
        }

        /**
        * @dev Returns one of the accounts that have `role`. `index` must be a
        * value between 0 and {getRoleMemberCount}, non-inclusive.
        *
        * Role bearers are not sorted in any particular way, and their ordering may
        * change at any point.
        *
        * WARNING: When using {getRoleMember} and {getRoleMemberCount}, make sure
        * you perform all queries on the same block. See the following
        * https://forum.openzeppelin.com/t/iterating-over-elements-on-enumerableset-in-openzeppelin-contracts/2296[forum post]
        * for more information.
        */
        function getRoleMember(bytes32 role, uint256 index)
            public
            view
            returns (address)
        {
            return _roles[role].members.at(index);
        }

        /**
        * @dev Returns the admin role that controls `role`. See {grantRole} and
        * {revokeRole}.
        *
        * To change a role's admin, use {_setRoleAdmin}.
        */
        function getRoleAdmin(bytes32 role) public view returns (bytes32) {
            return _roles[role].adminRole;
        }

        /**
        * @dev Grants `role` to `account`.
        *
        * If `account` had not been already granted `role`, emits a {RoleGranted}
        * event.
        *
        * Requirements:
        *
        * - the caller must have ``role``'s admin role.
        */
        function grantRole(bytes32 role, address account) public virtual {
            require(
                hasRole(_roles[role].adminRole, _msgSender()),
                "AccessControl: sender must be an admin to grant"
            );

            _grantRole(role, account);
        }

        /**
        * @dev Revokes `role` from `account`.
        *
        * If `account` had been granted `role`, emits a {RoleRevoked} event.
        *
        * Requirements:
        *
        * - the caller must have ``role``'s admin role.
        */
        function revokeRole(bytes32 role, address account) public virtual {
            require(
                hasRole(_roles[role].adminRole, _msgSender()),
                "AccessControl: sender must be an admin to revoke"
            );

            _revokeRole(role, account);
        }

        /**
        * @dev Revokes `role` from the calling account.
        *
        * Roles are often managed via {grantRole} and {revokeRole}: this function's
        * purpose is to provide a mechanism for accounts to lose their privileges
        * if they are compromised (such as when a trusted device is misplaced).
        *
        * If the calling account had been granted `role`, emits a {RoleRevoked}
        * event.
        *
        * Requirements:
        *
        * - the caller must be `account`.
        */
        function renounceRole(bytes32 role, address account) public virtual {
            require(
                account == _msgSender(),
                "AccessControl: can only renounce roles for self"
            );

            _revokeRole(role, account);
        }

        /**
        * @dev Grants `role` to `account`.
        *
        * If `account` had not been already granted `role`, emits a {RoleGranted}
        * event. Note that unlike {grantRole}, this function doesn't perform any
        * checks on the calling account.
        *
        * [WARNING]
        * ====
        * This function should only be called from the constructor when setting
        * up the initial roles for the system.
        *
        * Using this function in any other way is effectively circumventing the admin
        * system imposed by {AccessControl}.
        * ====
        */
        function _setupRole(bytes32 role, address account) internal virtual {
            _grantRole(role, account);
        }

        /**
        * @dev Sets `adminRole` as ``role``'s admin role.
        *
        * Emits a {RoleAdminChanged} event.
        */
        function _setRoleAdmin(bytes32 role, bytes32 adminRole) internal virtual {
            emit RoleAdminChanged(role, _roles[role].adminRole, adminRole);
            _roles[role].adminRole = adminRole;
        }

        function _grantRole(bytes32 role, address account) private {
            if (_roles[role].members.add(account)) {
                emit RoleGranted(role, account, _msgSender());
            }
        }

        function _revokeRole(bytes32 role, address account) private {
            if (_roles[role].members.remove(account)) {
                emit RoleRevoked(role, account, _msgSender());
            }
        }
    }

    // Partial License: MIT

    pragma solidity ^0.6.0;

    /**
    * @dev Standard math utilities missing in the Solidity language.
    */
    library Math {
        /**
        * @dev Returns the largest of two numbers.
        */
        function max(uint256 a, uint256 b) internal pure returns (uint256) {
            return a >= b ? a : b;
        }

        /**
        * @dev Returns the smallest of two numbers.
        */
        function min(uint256 a, uint256 b) internal pure returns (uint256) {
            return a < b ? a : b;
        }

        /**
        * @dev Returns the average of two numbers. The result is rounded towards
        * zero.
        */
        function average(uint256 a, uint256 b) internal pure returns (uint256) {
            // (a + b) / 2 can overflow, so we distribute
            return (a / 2) + (b / 2) + (((a % 2) + (b % 2)) / 2);
        }
    }

    // Partial License: MIT

    pragma solidity ^0.6.0;

    /**
    * @dev Collection of functions related to array types.
    */
    library Arrays {
        /**
        * @dev Searches a sorted `array` and returns the first index that contains
        * a value greater or equal to `element`. If no such index exists (i.e. all
        * values in the array are strictly less than `element`), the array length is
        * returned. Time complexity O(log n).
        *
        * `array` is expected to be sorted in ascending order, and to contain no
        * repeated elements.
        */
        function findUpperBound(uint256[] storage array, uint256 element)
            internal
            view
            returns (uint256)
        {
            if (array.length == 0) {
                return 0;
            }

            uint256 low = 0;
            uint256 high = array.length;

            while (low < high) {
                uint256 mid = Math.average(low, high);

                // Note that mid will always be strictly less than high (i.e. it will be a valid array index)
                // because Math.average rounds down (it does integer division with truncation).
                if (array[mid] > element) {
                    high = mid;
                } else {
                    low = mid + 1;
                }
            }

            // At this point `low` is the exclusive upper bound. We will return the inclusive upper bound.
            if (low > 0 && array[low - 1] == element) {
                return low - 1;
            } else {
                return low;
            }
        }
    }

    // Partial License: MIT

    pragma solidity ^0.6.0;

    /**
    * @title Counters
    * @author Matt Condon (@shrugs)
    * @dev Provides counters that can only be incremented or decremented by one. This can be used e.g. to track the number
    * of elements in a mapping, issuing ERC721 ids, or counting request ids.
    *
    * Include with `using Counters for Counters.Counter;`
    * Since it is not possible to overflow a 256 bit integer with increments of one, `increment` can skip the {SafeMath}
    * overflow check, thereby saving gas. This does assume however correct usage, in that the underlying `_value` is never
    * directly accessed.
    */
    library Counters {
        using SafeMath for uint256;

        struct Counter {
            // This variable should never be directly accessed by users of the library: interactions must be restricted to
            // the library's function. As of Solidity v0.5.2, this cannot be enforced, though there is a proposal to add
            // this feature: see https://github.com/ethereum/solidity/issues/4637
            uint256 _value; // default: 0
        }

        function current(Counter storage counter) internal view returns (uint256) {
            return counter._value;
        }

        function increment(Counter storage counter) internal {
            // The {SafeMath} overflow check can be skipped here, see the comment at the top
            counter._value += 1;
        }

        function decrement(Counter storage counter) internal {
            counter._value = counter._value.sub(1);
        }
    }

    // Partial License: MIT

    pragma solidity ^0.6.0;

    /**
    * @dev This contract extends an ERC20 token with a snapshot mechanism. When a snapshot is created, the balances and
    * total supply at the time are recorded for later access.
    *
    * This can be used to safely create mechanisms based on token balances such as trustless dividends or weighted voting.
    * In naive implementations it's possible to perform a "double spend" attack by reusing the same balance from different
    * accounts. By using snapshots to calculate dividends or voting power, those attacks no longer apply. It can also be
    * used to create an efficient ERC20 forking mechanism.
    *
    * Snapshots are created by the internal {_snapshot} function, which will emit the {Snapshot} event and return a
    * snapshot id. To get the total supply at the time of a snapshot, call the function {totalSupplyAt} with the snapshot
    * id. To get the balance of an account at the time of a snapshot, call the {balanceOfAt} function with the snapshot id
    * and the account address.
    *
    * ==== Gas Costs
    *
    * Snapshots are efficient. Snapshot creation is _O(1)_. Retrieval of balances or total supply from a snapshot is _O(log
    * n)_ in the number of snapshots that have been created, although _n_ for a specific account will generally be much
    * smaller since identical balances in subsequent snapshots are stored as a single entry.
    *
    * There is a constant overhead for normal ERC20 transfers due to the additional snapshot bookkeeping. This overhead is
    * only significant for the first transfer that immediately follows a snapshot for a particular account. Subsequent
    * transfers will have normal cost until the next snapshot, and so on.
    */
    abstract contract ERC20Snapshot is ERC20 {
        // Inspired by Jordi Baylina's MiniMeToken to record historical balances:
        // https://github.com/Giveth/minimd/blob/ea04d950eea153a04c51fa510b068b9dded390cb/contracts/MiniMeToken.sol

        using SafeMath for uint256;
        using Arrays for uint256[];
        using Counters for Counters.Counter;

        // Snapshotted values have arrays of ids and the value corresponding to that id. These could be an array of a
        // Snapshot struct, but that would impede usage of functions that work on an array.
        struct Snapshots {
            uint256[] ids;
            uint256[] values;
        }

        mapping(address => Snapshots) private _accountBalanceSnapshots;
        Snapshots private _totalSupplySnapshots;

        // Snapshot ids increase monotonically, with the first value being 1. An id of 0 is invalid.
        Counters.Counter private _currentSnapshotId;

        /**
        * @dev Emitted by {_snapshot} when a snapshot identified by `id` is created.
        */
        event Snapshot(uint256 id);

        /**
        * @dev Creates a new snapshot and returns its snapshot id.
        *
        * Emits a {Snapshot} event that contains the same id.
        *
        * {_snapshot} is `internal` and you have to decide how to expose it externally. Its usage may be restricted to a
        * set of accounts, for example using {AccessControl}, or it may be open to the public.
        *
        * [WARNING]
        * ====
        * While an open way of calling {_snapshot} is required for certain trust minimization mechanisms such as forking,
        * you must consider that it can potentially be used by attackers in two ways.
        *
        * First, it can be used to increase the cost of retrieval of values from snapshots, although it will grow
        * logarithmically thus rendering this attack ineffective in the long term. Second, it can be used to target
        * specific accounts and increase the cost of ERC20 transfers for them, in the ways specified in the Gas Costs
        * section above.
        *
        * We haven't measured the actual numbers; if this is something you're interested in please reach out to us.
        * ====
        */
        function _snapshot() internal virtual returns (uint256) {
            _currentSnapshotId.increment();

            uint256 currentId = _currentSnapshotId.current();
            emit Snapshot(currentId);
            return currentId;
        }

        /**
        * @dev Retrieves the balance of `account` at the time `snapshotId` was created.
        */
        function balanceOfAt(address account, uint256 snapshotId)
            public
            view
            returns (uint256)
        {
            (bool snapshotted, uint256 value) = _valueAt(
                snapshotId,
                _accountBalanceSnapshots[account]
            );

            return snapshotted ? value : balanceOf(account);
        }

        /**
        * @dev Retrieves the total supply at the time `snapshotId` was created.
        */
        function totalSupplyAt(uint256 snapshotId) public view returns (uint256) {
            (bool snapshotted, uint256 value) = _valueAt(
                snapshotId,
                _totalSupplySnapshots
            );

            return snapshotted ? value : totalSupply();
        }

        // _transfer, _mint and _burn are the only functions where the balances are modified, so it is there that the
        // snapshots are updated. Note that the update happens _before_ the balance change, with the pre-modified value.
        // The same is true for the total supply and _mint and _burn.
        function _transfer(
            address from,
            address to,
            uint256 value
        ) internal virtual override {
            _updateAccountSnapshot(from);
            _updateAccountSnapshot(to);

            super._transfer(from, to, value);
        }

        function _mint(address account, uint256 value) internal virtual override {
            _updateAccountSnapshot(account);
            _updateTotalSupplySnapshot();

            super._mint(account, value);
        }

        function _burn(address account, uint256 value) internal virtual override {
            _updateAccountSnapshot(account);
            _updateTotalSupplySnapshot();

            super._burn(account, value);
        }

        function _valueAt(uint256 snapshotId, Snapshots storage snapshots)
            private
            view
            returns (bool, uint256)
        {
            require(snapshotId > 0, "ERC20Snapshot: id is 0");
            // solhint-disable-next-line max-line-length
            require(
                snapshotId <= _currentSnapshotId.current(),
                "ERC20Snapshot: nonexistent id"
            );

            // When a valid snapshot is queried, there are three possibilities:
            //  a) The queried value was not modified after the snapshot was taken. Therefore, a snapshot entry was never
            //  created for this id, and all stored snapshot ids are smaller than the requested one. The value that corresponds
            //  to this id is the current one.
            //  b) The queried value was modified after the snapshot was taken. Therefore, there will be an entry with the
            //  requested id, and its value is the one to return.
            //  c) More snapshots were created after the requested one, and the queried value was later modified. There will be
            //  no entry for the requested id: the value that corresponds to it is that of the smallest snapshot id that is
            //  larger than the requested one.
            //
            // In summary, we need to find an element in an array, returning the index of the smallest value that is larger if
            // it is not found, unless said value doesn't exist (e.g. when all values are smaller). Arrays.findUpperBound does
            // exactly this.

            uint256 index = snapshots.ids.findUpperBound(snapshotId);

            if (index == snapshots.ids.length) {
                return (false, 0);
            } else {
                return (true, snapshots.values[index]);
            }
        }

        function _updateAccountSnapshot(address account) private {
            _updateSnapshot(_accountBalanceSnapshots[account], balanceOf(account));
        }

        function _updateTotalSupplySnapshot() private {
            _updateSnapshot(_totalSupplySnapshots, totalSupply());
        }

        function _updateSnapshot(Snapshots storage snapshots, uint256 currentValue)
            private
        {
            uint256 currentId = _currentSnapshotId.current();
            if (_lastSnapshotId(snapshots.ids) < currentId) {
                snapshots.ids.push(currentId);
                snapshots.values.push(currentValue);
            }
        }

        function _lastSnapshotId(uint256[] storage ids)
            private
            view
            returns (uint256)
        {
            if (ids.length == 0) {
                return 0;
            } else {
                return ids[ids.length - 1];
            }
        }
    }

    pragma solidity ^0.6.0;

    abstract contract CMERC20Snapshot is Context, AccessControl, ERC20Snapshot {
        bytes32 public constant SNAPSHOT_ROLE = keccak256("SNAPSHOT_ROLE");

        function snapshot() public {
            require(
                hasRole(SNAPSHOT_ROLE, _msgSender()),
                "ERC20Snapshot: must have snapshotter role to snapshot"
            );
            _snapshot();
        }
    }

    pragma solidity ^0.6.0;

    // imports

    contract FECORE is ERC20Burnable, CMERC20Snapshot {
        constructor(
            string memory name,
            string memory symbol,
            uint256 amount
        ) public payable ERC20(name, symbol) {
            _setupDecimals(18);
            _mint(msg.sender, amount);

            // set up required roles
            _setupRole(DEFAULT_ADMIN_ROLE, _msgSender());
            _setupRole(SNAPSHOT_ROLE, _msgSender());
        }

        // overrides
        function _burn(address account, uint256 value)
            internal
            override(ERC20, ERC20Snapshot)
        {
            super._burn(account, value);
        }

        function _mint(address account, uint256 value)
            internal
            override(ERC20, ERC20Snapshot)
        {
            super._mint(account, value);
        }

        function _transfer(
            address from,
            address to,
            uint256 value
        ) internal override(ERC20, ERC20Snapshot) {
            super._transfer(from, to, value);
        }
    }