interface IFYToken is IERC20 {
    /// @dev Asset that is returned on redemption.
    function underlying() external view returns (address);

    /// @dev Unix time at which redemption of fyToken for underlying are possible
    function maturity() external view returns (uint256);

    /// @dev Record price data at maturity
    function mature() external;

    /// @dev Mint fyToken providing an equal amount of underlying to the protocol
    function mintWithUnderlying(address to, uint256 amount) external;

    /// @dev Burn fyToken after maturity for an amount of underlying.
    function redeem(address to, uint256 amount) external returns (uint256);

    /// @dev Mint fyToken.
    /// This function can only be called by other Yield contracts, not users directly.
    /// @param to Wallet to mint the fyToken in.
    /// @param fyTokenAmount Amount of fyToken to mint.
    function mint(address to, uint256 fyTokenAmount) external;

    /// @dev Burn fyToken.
    /// This function can only be called by other Yield contracts, not users directly.
    /// @param from Wallet to burn the fyToken from.
    /// @param fyTokenAmount Amount of fyToken to burn.
    function burn(address from, uint256 fyTokenAmount) external;
}
function underlying() external view returns (address);

/// @dev Asset that is returned on redemption.