Input (grade 13): Libretti for operas, oratorios, and cantatas in the 17th and 18th centuries generally were written by someone other than the composer, often a well-known poet.
Output (grade 12): Two French writers called Henri Meilhac and Ludovic Halévy wrote a large number of opera and operetta libretti for the composers Jacques Offenbach, Jules Massenet and Georges Bizet.