interface IJoin {
    /// @dev asset managed by this contract
    function asset() external view returns (address);

    /// @dev Add tokens to this contract.
    function join(address user, uint128 wad) external returns (uint128);

    /// @dev Remove tokens to this contract.
    function exit(address user, uint128 wad) external returns (uint128);
}
function exit(address user, uint128 wad) external returns (uint128);

/// @dev Remove tokens to this contract.