Either you have a good sense of movies, or you are a good googler.
Good answer. How did you manage to get this one?
FYI to hide the answer and other tricks when posting see the "Click here for formatting codes (opens in a new window)" link at the lower bottom right of the screen in the editting window.[/q
I remembered that Casablanca was based on an play that was never performed (from the DVD commentary - and Laserdisc commentary before that). I looked on IMBD and there was the exact answer to the question.