fmod BOOK is
	protecting PAIR	*(sort Pair to Book)
			*(op pair to book)
			*(op getFirst to getTitle)
			*(op setFirst to setTitle)
			*(op getSecond to getAuthor)
			*(op setSecond to setAuthor) .

endfm

*** Example usage
red getTitle(book("The Guide", "Goethe")) .
red getTitle(setAuthor(setTitle(book("Thanks for all the fish", "Goethe"), "The Guide"), "Douglas Adams")) .