What is Copyleft?

[Fred Patrick]

> 
> A header that is pure API (only function declarations) are in 
> this class. The 
> names of the functions get copied over into the resulting object 
> file, but 
> the header file itself does not. I believe that there was a case 
> once that 
> ruled you couldn't copyright an API.
> 

Are there more details about not being able to copyright an API? 
Does API in this usage apply to CORBA interfaces as well?

If so it doesn't make much sense to me.
Fred Patrick