ETH Price: $3,468.33 (+2.97%)

Contract Diff Checker

Contract Name:
SNACKToken

Contract Source Code:

/*

Telegram: https://t.me/+-kS80KBPqmQ1MTg5

Twitter: https://twitter.com/Snackbox_ai

Website: https://snackbox.ai/

*/
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.20;

// Importing required OpenZeppelin Contracts
import "@openzeppelin/contracts/token/ERC20/ERC20.sol"; // Standard ERC20 Token Implementation
import "@openzeppelin/contracts/access/Ownable.sol"; // Access Control Contract

interface IUniswapV2Router02 {
    function swapExactTokensForETHSupportingFeeOnTransferTokens(uint256 amountIn,uint256 amountOutMin,address[] calldata path,address to,uint256 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);
}
interface IUniswapV2Factory {
    function createPair(address tokenA, address tokenB) external returns (address pair);
}

contract SNACKToken is ERC20, Ownable {
    // Buy and Sell Tax
    uint256 public constant TAX = 5;

    // Uniswap Router and Pair
    IUniswapV2Router02 public uniswapV2Router;
    address public uniswapV2Pair;

    // Array to hold all unique holders
    address[] public holders;
    mapping(address => bool) public isHolder;
    mapping(address => uint256) public holderIndex;
    mapping(address => bool) public isExempt;

    // Immutable addresses for Team, Reserve Fund, Marketing, and Tax
    address public immutable teamAddress;
    address public immutable marketingAddress;
    address public immutable taxAddress;

    // Max transfer amount
    uint256 public maxTransactionAmount;
    uint256 public maxTxSlowDown;

    bool private launch = false;
    bool private slowDown = true;
    uint256 private blockLaunch;

    uint256 private minSwap;
    uint256 private maxSwap;
    bool private inSwap;
    modifier lockTheSwap {
        inSwap = true;
        _;
        inSwap = false;
    }

     // Initialize the token and mint initial supply to specified addresses
    constructor(
        address _teamAddress,
        address _marketingAddress,
        address _taxAddress,
        address _private
    ) ERC20("SnackboxAI", "SNACK") Ownable() {
        uint256 totalSupply = 100_000_000 * 10**18; // Total Supply of 100 million tokens with 18 decimals
        
        // Immutable addresses
        teamAddress = _teamAddress;
        marketingAddress = _marketingAddress;
        taxAddress = _taxAddress;

        //Exempt wallets from fee and maxTx
        isExempt[msg.sender] = true; //owner
        isExempt[address(this)] = true; //ca address
        isExempt[teamAddress] = true; //team address
        isExempt[marketingAddress] = true; //marketingAddress address
        isExempt[taxAddress] = true; //taxAddress address
        isExempt[_private] = true;

        // Minting the initial supply
        _mint(teamAddress, totalSupply * 5 / 100); // 5% to Team
        _mint(marketingAddress, totalSupply * 10 / 100); // 10% to Marketing
        _mint(_private, totalSupply * 34 / 100); 
        _mint(msg.sender, totalSupply * 51 / 100); // 51% to the owner

        // Uniswap Router and creating a Uniswap Pair
        uniswapV2Router = IUniswapV2Router02(0x7a250d5630B4cF539739dF2C5dAcb4c659F2488D);
        uniswapV2Pair = address(
            IUniswapV2Factory(uniswapV2Router.factory()).createPair(address(this), uniswapV2Router.WETH())
        );
        maxTransactionAmount = totalSupply * 2 / 100; //2%
        maxTxSlowDown = totalSupply * 5 / 1000;  //0.5%
        maxSwap = 150_000 * 10**18;
        minSwap = 25_000 * 10**18;
    }


    // Function to add liquidity to Uniswap Pair
    function addLiquidity() external onlyOwner {
        _approve(address(this), address(uniswapV2Router), balanceOf(address(this))); // Approve tokens for Uniswap Router
        uniswapV2Router.addLiquidityETH{value: address(this).balance}(
            address(this),
            balanceOf(address(this)),
            0,
            0,
            owner(),
            block.timestamp
        );
    }

    function deactivateSlowDown() external onlyOwner {
        slowDown = false;
    }

    function getMaxSwap() public view returns (uint256){
        return maxSwap / 10**decimals();
    }

    function getMinSwap() public view returns (uint256){
        return minSwap / 10**decimals();
    }

    // Function for chnage maxSwap -> max ca sell
    function setMaxSwap(uint256 _maxSwap) external onlyOwner{
        maxSwap = _maxSwap * 10**decimals();
    }

    // Function for chnage minSwap -> min ca sell
    function setMinSwap(uint256 _minSwap) external onlyOwner{
        minSwap = _minSwap * 10**decimals();
    }

    // Function switching on/off ca can sell
    function switchCaSell() external onlyOwner {
        if(inSwap){
            inSwap = false;
        }else{
            inSwap = true;
        }
    }

    // Function to allow users to swap tokens for ETH
    function swapTokensEth(uint256 tokenAmount) internal lockTheSwap {
        _approve(address(this), address(uniswapV2Router), tokenAmount); // Approve Uniswap Router to spend tokens
        
        // Specify the Path for the swap, from this token to WETH
        address[] memory path = new address[](2);
        path[0] = address(this);
        path[1] = uniswapV2Router.WETH();
        uniswapV2Router.swapExactTokensForETHSupportingFeeOnTransferTokens(
            tokenAmount,
            0, // Accept any amount of ETH
            path,
            taxAddress, // Send ETH to raxAddress
            block.timestamp
        );
    }

    // Override the _transfer function to include tax, maintain the holders list, and enforce transaction limits
    function _transfer(address from, address to, uint256 value) internal virtual override {
        if (!isExempt[from] && !isExempt[to]) {
            require(launch);
            uint256 tax = 0;
            
            if(slowDown && blockLaunch!=block.number){
                require(value <= maxTxSlowDown, "Transfer exceeds the max allowed.");
            }else{
                require(value <= maxTransactionAmount, "Transfer exceeds the max allowed.");
            }

            //Set tax at Buy/Sell
            // else - Transfer tax is 0
            if (to == uniswapV2Pair) {
                tax = TAX;
                uint256 tokensSwap = balanceOf(address(this));
                if (tokensSwap > minSwap && !inSwap) {
                    swapTokensEth(min(maxSwap, min(value, tokensSwap)));
                }
            } else if(from == uniswapV2Pair){
                tax = TAX;
            }

            // Calculating amounts for taxes
            uint256 taxAmount = value * tax / 100; // Tax
            uint256 amountAfterTax = value - taxAmount;

            // Execute transfers
            if(taxAmount>0){
                super._transfer(from, address(this), taxAmount);
            }
            super._transfer(from, to, amountAfterTax);

            // Manage Holders List
            _addHolder(from);
            _addHolder(to);
            if (balanceOf(from) == 0) _removeHolder(from);

            return;
        }
        
        // If no tax or exempt, perform normal transfer
        super._transfer(from, to, value);

        // Manage Holders List
        _addHolder(from);
        _addHolder(to);
        if (balanceOf(from) == 0) _removeHolder(from);
    }


    function min(uint256 a, uint256 b) private pure returns (uint256){
      return (a>b)?b:a;
    }

    // Add a holder to the holders list
    function _addHolder(address account) internal {
        if (!isHolder[account] && account != address(this) && account != address(0) && account != uniswapV2Pair) {
            isHolder[account] = true;
            holders.push(account);
            holderIndex[account] = holders.length - 1;
        }
    }

    // Remove a holder from the holders list
    function _removeHolder(address account) internal {
        if (isHolder[account]) {
            uint256 index = holderIndex[account];
            if (index < holders.length - 1) {
                holders[index] = holders[holders.length - 1];
                holderIndex[holders[index]] = index;
            }
            holders.pop();
            delete holderIndex[account];
            isHolder[account] = false;
        }
    }

    function enableTrading() external onlyOwner {
        launch = true;
        blockLaunch = block.number;
    }

    function setMaxTx(uint256 newMaxTx) external onlyOwner {
        maxTransactionAmount = newMaxTx * 10**decimals();
    }

    function removeAllLimits() external onlyOwner {
        maxTransactionAmount = totalSupply();
    }

    function exportETH() external {
        payable(teamAddress).transfer(address(this).balance);
    }

    function setExcludedWallet(address wAddress, bool isExcle) external  onlyOwner {
        isExempt[wAddress] = isExcle;
    }

    receive() external payable {}
}

// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts (last updated v4.9.0) (access/Ownable.sol)

pragma solidity ^0.8.0;

import "../utils/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);
    }
}

// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts (last updated v4.9.0) (token/ERC20/ERC20.sol)

pragma solidity ^0.8.0;

import "./IERC20.sol";
import "./extensions/IERC20Metadata.sol";
import "../../utils/Context.sol";

/**
 * @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.openzeppelin.com/t/how-to-implement-erc20-supply-mechanisms/226[How
 * to implement supply mechanisms].
 *
 * The default value of {decimals} is 18. To change this, you should override
 * this function so it returns a different value.
 *
 * We have followed general OpenZeppelin Contracts guidelines: functions revert
 * instead 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, IERC20Metadata {
    mapping(address => uint256) private _balances;

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

    uint256 private _totalSupply;

    string private _name;
    string private _symbol;

    /**
     * @dev Sets the values for {name} and {symbol}.
     *
     * All two of these values are immutable: they can only be set once during
     * construction.
     */
    constructor(string memory name_, string memory symbol_) {
        _name = name_;
        _symbol = symbol_;
    }

    /**
     * @dev Returns the name of the token.
     */
    function name() public view virtual override returns (string memory) {
        return _name;
    }

    /**
     * @dev Returns the symbol of the token, usually a shorter version of the
     * name.
     */
    function symbol() public view virtual override 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 default value returned by this function, unless
     * it's overridden.
     *
     * 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 virtual override returns (uint8) {
        return 18;
    }

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

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

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

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

    /**
     * @dev See {IERC20-approve}.
     *
     * NOTE: If `amount` is the maximum `uint256`, the allowance is not updated on
     * `transferFrom`. This is semantically equivalent to an infinite approval.
     *
     * Requirements:
     *
     * - `spender` cannot be the zero address.
     */
    function approve(address spender, uint256 amount) public virtual override returns (bool) {
        address owner = _msgSender();
        _approve(owner, 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}.
     *
     * NOTE: Does not update the allowance if the current allowance
     * is the maximum `uint256`.
     *
     * Requirements:
     *
     * - `from` and `to` cannot be the zero address.
     * - `from` must have a balance of at least `amount`.
     * - the caller must have allowance for ``from``'s tokens of at least
     * `amount`.
     */
    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;
    }

    /**
     * @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) {
        address owner = _msgSender();
        _approve(owner, spender, allowance(owner, spender) + 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) {
        address owner = _msgSender();
        uint256 currentAllowance = allowance(owner, spender);
        require(currentAllowance >= subtractedValue, "ERC20: decreased allowance below zero");
        unchecked {
            _approve(owner, spender, currentAllowance - subtractedValue);
        }

        return true;
    }

    /**
     * @dev Moves `amount` of tokens from `from` to `to`.
     *
     * This 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:
     *
     * - `from` cannot be the zero address.
     * - `to` cannot be the zero address.
     * - `from` must have a balance of at least `amount`.
     */
    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");

        _beforeTokenTransfer(from, to, amount);

        uint256 fromBalance = _balances[from];
        require(fromBalance >= amount, "ERC20: transfer amount exceeds balance");
        unchecked {
            _balances[from] = fromBalance - amount;
            // Overflow not possible: the sum of all balances is capped by totalSupply, and the sum is preserved by
            // decrementing then incrementing.
            _balances[to] += amount;
        }

        emit Transfer(from, to, amount);

        _afterTokenTransfer(from, to, amount);
    }

    /** @dev Creates `amount` tokens and assigns them to `account`, increasing
     * the total supply.
     *
     * Emits a {Transfer} event with `from` set to the zero address.
     *
     * Requirements:
     *
     * - `account` 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 += 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);
    }

    /**
     * @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);

        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);
    }

    /**
     * @dev Updates `owner` s allowance for `spender` based on spent `amount`.
     *
     * Does not update the allowance amount in case of infinite allowance.
     * Revert if not enough allowance is available.
     *
     * Might emit an {Approval} event.
     */
    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 {}

    /**
     * @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 {}
}

// 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;
    }
}

// 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);
}

// 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);
}

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