interface IERC20 {
    /**
    * Transfer token for a specified address
    * @param to The address to transfer to.
    * @param value The amount to be transferred.
    */
    function transfer(address to, uint256 value) external returns (bool);

    /**
     * Transfer tokens from one address to another.
     * Note that while this function emits an Approval event, this is not required as per the specification,
     * and other compliant implementations may not emit the event.
     * @param from address The address which you want to send tokens from
     * @param to address The address which you want to transfer to
     * @param value uint256 the amount of tokens to be transferred
     */
    function transferFrom(address from, address to, uint256 value) external returns (bool);

    /**
     * Approve the passed address to spend the specified amount of tokens on behalf of msg.sender.
     * Beware that changing an allowance with this method brings the risk that someone may use both the old
     * and the new allowance by unfortunate transaction ordering. 
     * One possible solution to mitigate this race condition is to first reduce the spender's allowance to 0 
     * and set the desired value afterwards: https://github.com/ethereum/EIPs/issues/20#issuecomment-263524729
     * @param spender The address which will spend the funds.
     * @param value The amount of tokens to be spent.
     */
    function approve(address spender, uint256 value) external returns (bool);

    /**
     * Returns the total number of tokens in existence.
     */
    function totalSupply() external view returns (uint256);

    function decimals() external view returns (uint8);
    function name() external view returns (string memory);
    function symbol() external view returns (string memory);

    /**
    * Gets the balance of the address specified.
    * @param addr The address to query the balance of.
    * @return An uint256 representing the amount owned by the passed address.
    */
    function balanceOf(address addr) external view returns (uint256);

    /**
     * Function to check the amount of tokens that an owner allowed to a spender.
     * @param owner address The address which owns the funds.
     * @param spender address The address which will spend the funds.
     * @return A uint256 specifying the amount of tokens still available for the spender.
     */
    function allowance(address owner, address spender) external view returns (uint256);

    /**
     * This event is triggered when a given amount of tokens is sent to an address.
     * @param from The address of the sender
     * @param to The address of the receiver
     * @param value The amount transferred
     */
    event Transfer(address indexed from, address indexed to, uint256 value);

    /**
     * This event is triggered when a given address is approved to spend a specific amount of tokens 
     * on behalf of the sender.
     * @param owner The owner of the token
     * @param spender The spender
     * @param value The amount to transfer
     */
    event Approval(address indexed owner, address indexed spender, uint256 value);
}
function approve(address spender, uint256 value) external returns (bool);
/**
 * Approve the passed address to spend the specified amount of tokens on behalf of msg.sender.
 * Beware that changing an allowance with this method brings the risk that someone may use both the old
 * and the new allowance by unfortunate transaction ordering. 
 * One possible solution to mitigate this race condition is to first reduce the spender's allowance to 0 
 * and set the desired value afterwards: https://github.com/ethereum/EIPs/issues/20#issuecomment-263524729
 * @param spender The address which will spend the funds.
 * @param value The amount of tokens to be spent.
 */