interface IPeripheryImmutableState {
    /// @return Returns the address of the Uniswap V3 factory
    function factory() external view returns (address);

    /// @return Returns the address of WETH9
    function WETH9() external view returns (address);
}
/// @title Immutable state
/// @notice Functions that return immutable state of the router
function WETH9() external view returns (address);

/// @return Returns the address of WETH9