4) The fourth file is called 'messages.i'. It contains all the standard predefined runtime messages in the ALAN language in one place, for easy modification. For example, if you want to change the default "You can't go that way" message, you just need to locate the appropriate message (in this case 'noway') in the list and change the message inside the quotes: 

MESSAGE
    ...
    NOWAY: "There is nothing interesting in that direction."

There is also a sample game included with the library distribution, for the IF author to be able to test different responses and object behaviour.