interface IErc20 {
    /// EVENTS ///

    /// @notice Emitted when an approval happens.
    /// @param owner The address of the owner of the tokens.
    /// @param spender The address of the spender.
    /// @param amount The maximum amount that can be spent.
    event Approval(address indexed owner, address indexed spender, uint256 amount);

    /// @notice Emitted when a transfer happens.
    /// @param from The account sending the tokens.
    /// @param to The account receiving the tokens.
    /// @param amount The amount of tokens transferred.
    event Transfer(address indexed from, address indexed to, uint256 amount);

    /// CONSTANT FUNCTIONS ///

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

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

    /// @notice Returns the number of decimals used to get its user representation.
    function decimals() external view returns (uint8);

    /// @notice Returns the name of the token.
    function name() external view returns (string memory);

    /// @notice Returns the symbol of the token, usually a shorter version of the name.
    function symbol() external view returns (string memory);

    /// @notice Returns the amount of tokens in existence.
    function totalSupply() external view returns (uint256);

    /// NON-CONSTANT FUNCTIONS ///

    /// @notice Sets `amount` as the allowance of `spender` over the caller's tokens.
    ///
    /// @dev Emits an {Approval} event.
    ///
    /// 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
    ///
    /// Requirements:
    ///
    /// - `spender` cannot be the zero address.
    ///
    /// @return a boolean value indicating whether the operation succeeded.
    function approve(address spender, uint256 amount) external returns (bool);

    /// @notice Atomically decreases the allowance granted to `spender` by the caller.
    ///
    /// @dev Emits an {Approval} event indicating the updated allowance.
    ///
    /// This is an alternative to {approve} that can be used as a mitigation for problems described
    /// in {Erc20Interface-approve}.
    ///
    /// Requirements:
    ///
    /// - `spender` cannot be the zero address.
    /// - `spender` must have allowance for the caller of at least `subtractedValue`.
    function decreaseAllowance(address spender, uint256 subtractedValue) external returns (bool);

    /// @notice Atomically increases the allowance granted to `spender` by the caller.
    ///
    /// @dev Emits an {Approval} event indicating the updated allowance.
    ///
    /// This is an alternative to {approve} that can be used as a mitigation for the problems described above.
    ///
    /// Requirements:
    ///
    /// - `spender` cannot be the zero address.
    function increaseAllowance(address spender, uint256 addedValue) external returns (bool);

    /// @notice Moves `amount` tokens from the caller's account to `recipient`.
    ///
    /// @dev Emits a {Transfer} event.
    ///
    /// Requirements:
    ///
    /// - `recipient` cannot be the zero address.
    /// - The caller must have a balance of at least `amount`.
    ///
    /// @return a boolean value indicating whether the operation succeeded.
    function transfer(address recipient, uint256 amount) external returns (bool);

    /// @notice Moves `amount` tokens from `sender` to `recipient` using the allowance mechanism. `amount`
    /// `is then deducted from the caller's allowance.
    ///
    /// @dev Emits a {Transfer} event and an {Approval} event indicating the updated allowance. This is
    /// not required by the Erc. 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 approed `sender` to spent at least `amount` tokens.
    ///
    /// @return a boolean value indicating whether the operation succeeded.
    function transferFrom(
        address sender,
        address recipient,
        uint256 amount
    ) external returns (bool);
}
/// @title IErc20
/// @author Paul Razvan Berg
/// @notice Implementation for the Erc20 standard.
///
/// 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 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 Erc 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.
///
/// @dev Forked from OpenZeppelin
/// https://github.com/OpenZeppelin/openzeppelin-contracts/blob/v3.4.0/contracts/token/ERC20/ERC20.sol
function totalSupply() external view returns (uint256);

/// @notice Returns the amount of tokens in existence.